feat(tabs): adds the md-tab-group component

src/components/tab-group/ink-bar.ts

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+import {Directive, Renderer, ElementRef} from '@angular/core';
+
+/**
+ * The ink-bar is used to display and animate the line underneath the current active tab label.
+ * @internal
+ */
+@Directive({
+  selector: 'md-ink-bar',
+})
+export class MdInkBar {
+  constructor(private _renderer: Renderer, private _elementRef: ElementRef) {}
+
+  /**
+   * Calculates the styles from the provided element in order to align the ink-bar to that element.
+   * @param element
+   */
+  alignToElement(element: HTMLElement) {
+    this._renderer.setElementStyle(this._elementRef.nativeElement, 'left',
+        this._getLeftPosition(element));
+    this._renderer.setElementStyle(this._elementRef.nativeElement, 'width',
+        this._getElementWidth(element));
+  }
+
+  /**
+   * Generates the pixel distance from the left based on the provided element in string format.
+   * @param element
+   * @returns {string}
+   */
+  private _getLeftPosition(element: HTMLElement): string {
+    return element.offsetLeft + 'px';
+  }
+
+  /**
+   * Generates the pixel width from the provided element in string format.
+   * @param element
+   * @returns {string}
+   */
+  private _getElementWidth(element: HTMLElement): string {
+    return element.offsetWidth + 'px';
+  }
+}

src/components/tab-group/tab-content.ts

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+import {Directive, TemplateRef, ViewContainerRef} from '@angular/core';
+import {TemplatePortalDirective} from '../../core/portal/portal-directives';
+
+/** Used to flag tab contents for use with the portal directive */
+@Directive({
+  selector: '[md-tab-content]'
+})
+export class MdTabContent extends TemplatePortalDirective {
+  constructor(templateRef: TemplateRef<any>, viewContainerRef: ViewContainerRef) {
+    super(templateRef, viewContainerRef);
+  }
+}

src/components/tab-group/tab-group.html

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+<div class="md-tab-header" role="tablist"
+     (keydown.arrowRight)="focusNextTab()"
+     (keydown.arrowLeft)="focusPreviousTab()"
+     (keydown.enter)="selectedIndex = focusIndex">
+  <div class="md-tab-label" role="tab" md-tab-label-wrapper
+       *ngFor="let label of labels; let i = index"
+       [id]="getTabLabelId(i)"
+       [tabIndex]="selectedIndex == i ? 0 : -1"
+       [attr.aria-controls]="getTabContentId(i)"
+       [attr.aria-selected]="selectedIndex == i"
+       [class.md-active]="selectedIndex == i"
+       (click)="focusIndex = selectedIndex = i">
+    <template [portalHost]="label"></template>
+  </div>
+  <md-ink-bar></md-ink-bar>
+</div>
+<div class="md-tab-body-wrapper">
+  <div class="md-tab-body"
+       *ngFor="let content of contents; let i = index"
+       [id]="getTabContentId(i)"
+       [class.md-active]="selectedIndex == i"
+       [attr.aria-labelledby]="getTabLabelId(i)">
+    <template role="tabpanel" [portalHost]="content" *ngIf="selectedIndex == i"></template>
+  </div>
+</div>

src/components/tab-group/tab-group.scss

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+@import 'variables';
+@import 'default-theme';
+
+$md-tab-bar-height: 48px !default;
+
+:host {
+  display: block;
+  font-family: $md-font-family;
+}
+
+/** The top section of the view; contains the tab labels */
+.md-tab-header {
+  overflow: hidden;
+  position: relative;
+  display: flex;
+  flex-direction: row;
+  border-bottom: 1px solid md-color($md-background, status-bar);
+}
+
+/** Wraps each tab label */
+.md-tab-label {
+  line-height: $md-tab-bar-height;
+  height: $md-tab-bar-height;
+  padding: 0 12px;
+  font-size: $md-body-font-size-base;
+  font-family: $md-font-family;
+  font-weight: 500;
+  cursor: pointer;
+  box-sizing: border-box;
+  color: currentColor;
+  opacity: 0.6;
+  min-width: 160px;
+  text-align: center;
+  &:focus {
+    outline: none;
+    opacity: 1;
+    background-color: md-color($md-primary, 100, 0.3);
+  }
+}
+
+/** The bottom section of the view; contains the tab bodies */
+.md-tab-body-wrapper {
+  position: relative;
+  height: 200px;
+  overflow: hidden;
+  padding: 12px;
+}
+
+/** Wraps each tab body */
+.md-tab-body {
+  display: none;
+  &.md-active {
+    display: block;
+  }
+}
+
+/** The colored bar that underlines the active tab */
+md-ink-bar {
+  position: absolute;
+  bottom: 0;
+  height: 2px;
+  background-color: md-color($md-primary, 500);
+  transition: 0.35s ease-out;
+}

src/components/tab-group/tab-group.spec.ts

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+import {
+    it,
+    expect,
+    beforeEach,
+    inject,
+    describe,
+    async
+} from '@angular/core/testing';
+import {TestComponentBuilder, ComponentFixture} from '@angular/compiler/testing';
+import {MD_TAB_GROUP_DIRECTIVES, MdTabGroup} from './tab-group';
+import {Component} from '@angular/core';
+import {By} from '@angular/platform-browser';
+
+describe('MdTabGroup', () => {
+  let builder: TestComponentBuilder;
+  let fixture: ComponentFixture<SimpleTabsTestApp>;
+
+  beforeEach(inject([TestComponentBuilder], (tcb: TestComponentBuilder) => {
+    builder = tcb;
+  }));
+
+  describe('basic behavior', () => {
+    beforeEach(async(() => {
+      builder.createAsync(SimpleTabsTestApp).then(f => {
+        fixture = f;
+      });
+    }));
+
+    it('should default to the first tab', () => {
+      checkSelectedIndex(1);
+    });
+
+    it('should change selected index on click', () => {
+      let component = fixture.debugElement.componentInstance;
+      component.selectedIndex = 0;
+      checkSelectedIndex(0);
+
+      // select the second tab
+      let tabLabel = fixture.debugElement.query(By.css('.md-tab-label:nth-of-type(2)'));
+      tabLabel.nativeElement.click();
+      checkSelectedIndex(1);
+
+      // select the third tab
+      tabLabel = fixture.debugElement.query(By.css('.md-tab-label:nth-of-type(3)'));
+      tabLabel.nativeElement.click();
+      checkSelectedIndex(2);
+    });
+
+    it('should cycle through tab focus with focusNextTab/focusPreviousTab functions', () => {
+      let tabComponent = fixture.debugElement.query(By.css('md-tab-group')).componentInstance;
+      tabComponent.focusIndex = 0;
+      fixture.detectChanges();
+      expect(tabComponent.focusIndex).toBe(0);
+
+      tabComponent.focusNextTab();
+      fixture.detectChanges();
+      expect(tabComponent.focusIndex).toBe(1);
+
+      tabComponent.focusNextTab();
+      fixture.detectChanges();
+      expect(tabComponent.focusIndex).toBe(2);
+
+      tabComponent.focusNextTab();
+      fixture.detectChanges();
+      expect(tabComponent.focusIndex).toBe(2); // should stop at 2
+
+      tabComponent.focusPreviousTab();
+      fixture.detectChanges();
+      expect(tabComponent.focusIndex).toBe(1);
+
+      tabComponent.focusPreviousTab();
+      fixture.detectChanges();
+      expect(tabComponent.focusIndex).toBe(0);
+
+      tabComponent.focusPreviousTab();
+      fixture.detectChanges();
+      expect(tabComponent.focusIndex).toBe(0); // should stop at 0
+    });
+
+    it('should change tabs based on selectedIndex', () => {
+      let component = fixture.debugElement.componentInstance;
+      checkSelectedIndex(1);
+
+      component.selectedIndex = 2;
+      checkSelectedIndex(2);
+    });
+  });
+
+  /**
+   * Checks that the `selectedIndex` has been updated; checks that the label and body have the
+   * `md-active` class
+   */
+  function checkSelectedIndex(index: number) {
+    fixture.detectChanges();
+
+    let tabComponent: MdTabGroup = fixture.debugElement
+        .query(By.css('md-tab-group')).componentInstance;
+    expect(tabComponent.selectedIndex).toBe(index);
+
+    let tabLabelElement = fixture.debugElement
+        .query(By.css(`.md-tab-label:nth-of-type(${index + 1})`)).nativeElement;
+    expect(tabLabelElement.classList.contains('md-active')).toBe(true);
+
+    let tabContentElement = fixture.debugElement
+        .query(By.css(`#${tabLabelElement.id}`)).nativeElement;
+    expect(tabContentElement.classList.contains('md-active')).toBe(true);
+  }
+});
+
+@Component({
+  selector: 'test-app',
+  template: `
+    <md-tab-group class="tab-group" [selectedIndex]="selectedIndex">
+      <md-tab>
+        <template md-tab-label>Tab One</template>
+        <template md-tab-content>Tab one content</template>
+      </md-tab>
+      <md-tab>
+        <template md-tab-label>Tab Two</template>
+        <template md-tab-content>Tab two content</template>
+      </md-tab>
+      <md-tab>
+        <template md-tab-label>Tab Three</template>
+        <template md-tab-content>Tab three content</template>
+      </md-tab>
+    </md-tab-group>
+  `,
+  directives: [MD_TAB_GROUP_DIRECTIVES]
+})
+class SimpleTabsTestApp {
+  selectedIndex: number = 1;
+}

src/components/tab-group/tab-group.ts

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+import {Component, Input, ViewChildren, NgZone} from '@angular/core';
+import {QueryList} from '@angular/core';
+import {ContentChildren} from '@angular/core';
+import {PortalHostDirective} from '../../core/portal/portal-directives';
+import {MdTabLabel} from './tab-label';
+import {MdTabContent} from './tab-content';
+import {MdTabLabelWrapper} from './tab-label-wrapper';
+import {MdInkBar} from './ink-bar';
+
+/** Used to generate unique ID's for each tab component */
+let nextId = 0;
+
+/**
+ * Material design tab-group component.  Supports basic tab pairs (label + content) and includes
+ * animated ink-bar, keyboard navigation, and screen reader.
+ * See: https://www.google.com/design/spec/components/tabs.html
+ */
+@Component({
+  selector: 'md-tab-group',
+  templateUrl: './components/tab-group/tab-group.html',
+  styleUrls: ['./components/tab-group/tab-group.css'],
+  directives: [PortalHostDirective, MdTabLabelWrapper, MdInkBar],
+})
+export class MdTabGroup {
+  /** @internal */
+  @ContentChildren(MdTabLabel) labels: QueryList<MdTabLabel>;
+
+  /** @internal */
+  @ContentChildren(MdTabContent) contents: QueryList<MdTabContent>;
+
+  @ViewChildren(MdTabLabelWrapper) private _labelWrappers: QueryList<MdTabLabelWrapper>;
+  @ViewChildren(MdInkBar) private _inkBar: QueryList<MdInkBar>;
+
+  @Input() selectedIndex: number = 0;
+
+  private _focusIndex: number = 0;
+  private _groupId: number;
+
+  constructor(private _zone: NgZone) {
+    this._groupId = nextId++;
+  }
+
+  /**
+   * Waits one frame for the view to update, then upates the ink bar
+   * Note: This must be run outside of the zone or it will create an infinite change detection loop
+   * @internal
+   */
+  ngAfterViewChecked(): void {
+    this._zone.runOutsideAngular(() => {
+      window.requestAnimationFrame(() => {
+        this._updateInkBar();
+      });
+    });
+  }
+
+  /** Tells the ink-bar to align itself to the current label wrapper */
+  private _updateInkBar(): void {
+    this._inkBar.toArray()[0].alignToElement(this._currentLabelWrapper);
+  }
+
+  /**
+   * Reference to the current label wrapper; defaults to null for initial render before the
+   * ViewChildren references are ready.
+   */
+  private get _currentLabelWrapper(): HTMLElement {
+    return this._labelWrappers
+        ? this._labelWrappers.toArray()[this.selectedIndex].elementRef.nativeElement
+        : null;
+  }
+
+  /** Tracks which element has focus; used for keyboard navigation */
+  get focusIndex(): number {
+    return this._focusIndex;
+  }
+
+  /** When the focus index is set, we must manually send focus to the correct label */
+  set focusIndex(value: number) {
+    this._focusIndex = value;
+    if (this._labelWrappers && this._labelWrappers.length) {
+      this._labelWrappers.toArray()[value].focus();
+    }
+  }
+
+  /**
+   * Returns a unique id for each tab label element
+   * @internal
+   */
+  getTabLabelId(i: number): string {
+    return `md-tab-label-${this._groupId}-${i}`;
+  }
+
+  /**
+   * Returns a unique id for each tab content element
+   * @internal
+   */
+  getTabContentId(i: number): string {
+    return `md-tab-content-${this._groupId}-${i}`;
+  }
+
+  /** Increment the focus index by 1; prevent going over the number of tabs */
+  focusNextTab(): void {
+    if (this._labelWrappers && this.focusIndex < this._labelWrappers.length - 1) {
+      this.focusIndex++;
+    }
+  }
+
+  /** Decrement the focus index by 1; prevent going below 0 */
+  focusPreviousTab(): void {
+    if (this.focusIndex > 0) {
+      this.focusIndex--;
+    }
+  }
+}
+
+export const MD_TAB_GROUP_DIRECTIVES = [MdTabGroup, MdTabLabel, MdTabContent];