perf(view cache): Avoid http.get

This change makes templateUrl component creation 100% faster.

It is a stop-gap until #1107 is fixed.

Closes #1108

benchmark/web/tree-tmpl.html

@@ -0,0 +1,4 @@
+<span> {{ctrl.data.value}}
+   <span ng-if="ctrl.data.right != null"><tree-url data=ctrl.data.right></span>
+   <span ng-if="ctrl.data.left != null"><tree-url data=ctrl.data.left></span>
+</span>

benchmark/web/tree.dart

@@ -19,6 +19,15 @@ class TreeComponent {
   var data;
 }
 
+@Component(
+    selector: 'tree-url',
+    templateUrl: 'tree-tmpl.html',
+    publishAs: 'ctrl')
+class TreeUrlComponent {
+  @NgOneWay('data')
+  var data;
+}
+
 
 // This is a baseline implementation of TreeComponent.
 // It assumes the data never changes and simply throws elements on the DOM
@@ -239,6 +248,7 @@ main() {
 
   var module = new Module()
       ..type(TreeComponent)
+      ..type(TreeUrlComponent)
       ..type(NgFreeTree)
       ..type(NgFreeTreeScoped)
       ..type(NgFreeTreeClass)

benchmark/web/tree.html

@@ -14,12 +14,14 @@
   </p>
 
   <div>Default: <input type=checkbox ng-model="useDefault"></div>
+  <div>From URL: <input type=checkbox ng-model="useUrl"></div>
   <div>Baseline: <input type=checkbox ng-model="useBaseline"></div>
   <div>Baseline + scope: <input type=checkbox ng-model="useBaselineScoped"></div>
   <div>Baseline + class: <input type=checkbox ng-model="useBaselineClass"></div>
 
 
   <tree ng-if="useDefault" data=initData></tree>
+  <tree-url ng-if="useUrl" data=initData></tree-url>
 
   <ng-free-tree ng-if="useBaseline" data=initData></ng-free-tree>
   <ng-free-tree-scoped ng-if="useBaselineScoped" data=initData></ng-free-tree-scoped>

lib/core_dom/view_factory.dart

@@ -118,6 +118,7 @@ class WalkingViewFactory implements ViewFactory {
 @Injectable()
 class ViewCache {
   // _viewFactoryCache is unbounded
+  // This cache contains both HTML and URL keys.
   final viewFactoryCache = new LruCache<String, ViewFactory>();
   final Http http;
   final TemplateCache templateCache;
@@ -138,8 +139,15 @@ class ViewCache {
   }
 
   async.Future<ViewFactory> fromUrl(String url, DirectiveMap directives) {
-    return http.get(url, cache: templateCache).then(
-        (resp) => fromHtml(resp.responseText, directives));
+    ViewFactory viewFactory = viewFactoryCache.get(url);
+    if (viewFactory == null) {
+      return http.get(url, cache: templateCache).then((resp) {
+        var viewFactoryFromHttp = fromHtml(resp.responseText, directives);
+        viewFactoryCache.put(url, viewFactoryFromHttp);
+        return viewFactoryFromHttp;
+      });
+    }
+    return new async.Future.value(viewFactory);
   }
 }
 

lib/core_dom/web_platform.dart

@@ -91,7 +91,14 @@ class PlatformViewCache implements ViewCache {
   }
 
   async.Future<ViewFactory> fromUrl(String url, DirectiveMap directives) {
-    return http.get(url, cache: templateCache).then(
-            (resp) => fromHtml(resp.responseText, directives));
+    ViewFactory viewFactory = viewFactoryCache.get(url);
+    if (viewFactory == null) {
+      return http.get(url, cache: templateCache).then((resp) {
+        var viewFactoryFromHttp = fromHtml(resp.responseText, directives);
+        viewFactoryCache.put(url, viewFactoryFromHttp);
+        return viewFactoryFromHttp;
+      });
+    }
+    return new async.Future.value(viewFactory);
   }
 }

test/core/templateurl_spec.dart

@@ -269,15 +269,9 @@ void main() {
             '<style>.hello{}</style><div log="SIMPLE">Simple!</div>'
         );
 
-        // Since the template cache is disabled, we expect a 'simple.html' call.
-        backend
-          ..expectGET('simple.html').respond(200, '<div log="SIMPLE">Simple!</div>');
-
         var element2 = e('<div><html-and-css>ignore</html-and-css><div>');
         compile([element2], directives)(injector, [element2]);
 
-        microLeap();
-        backend.flush();
         microLeap();
 
         expect(element2.children[0].shadowRoot).toHaveHtml(