perf: speed up shallowCopy and special case Attributes cloning

`for in` is much faster than `Object.keys()` but `for in` includes properties from the prototype.

http://jsperf.com/for-in-vs-object-keys2

All the uses of shallowCopy don't deal with objects with heavy prototypes, except for Attributes instances
in $compile.

For this reason it's better to special-case Attributes constructor and make it do it's own shallow copy.
This cleans up the Attribute/$compile code as well.

Author: IgorMinar

src/Angular.js

@@ -821,11 +821,13 @@ function copy(source, destination, stackSource, stackDest) {
 }
 
 /**
- * Creates a shallow copy of an object, an array or a primitive
+ * Creates a shallow copy of an object, an array or a primitive.
+ *
+ * Assumes that there no proto properties for objects
  */
 function shallowCopy(src, dst) {
   var i = 0;
-  var l;
+  var l, key;
 
   if (isArray(src)) {
     dst = dst || [];
@@ -836,11 +838,7 @@ function shallowCopy(src, dst) {
   } else if (isObject(src)) {
     dst = dst || {};
 
-    var keys = Object.keys(src);
-
-    for (l = keys.length; i < l; i++) {
-      var key = keys[i];
-
+    for (key in src) {
       if (!(key.charAt(0) === '$' && key.charAt(1) === '$')) {
         dst[key] = src[key];
       }

src/ng/compile.js

@@ -663,9 +663,20 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
     function($injector,   $interpolate,   $exceptionHandler,   $http,   $templateCache,   $parse,
              $controller,   $rootScope,   $document,   $sce,   $animate,   $$sanitizeUri) {
 
-    var Attributes = function(element, attr) {
+    var Attributes = function(element, attributesToCopy) {
+      if (attributesToCopy) {
+        var keys = Object.keys(attributesToCopy);
+        var i, l, key;
+
+        for (i = 0, l = keys.length; i < l; i++) {
+          key = keys[i];
+          this[key] = attributesToCopy[key];
+        }
+      } else {
+        this.$attr = {};
+      }
+
       this.$$element = element;
-      this.$attr = attr || {};
     };
 
     Attributes.prototype = {
@@ -1459,12 +1470,12 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
 
 
       function nodeLinkFn(childLinkFn, scope, linkNode, $rootElement, boundTranscludeFn) {
-        var attrs, $element, i, ii, linkFn, controller, isolateScope, elementControllers = {}, transcludeFn;
+        var i, ii, linkFn, controller, isolateScope, elementControllers = {}, transcludeFn;
 
-        attrs = (compileNode === linkNode)
-          ? templateAttrs
-          : shallowCopy(templateAttrs, new Attributes(jqLite(linkNode), templateAttrs.$attr));
-        $element = attrs.$$element;
+        var $element = jqLite(linkNode);
+        var attrs = (compileNode === linkNode)
+              ? templateAttrs
+              : new Attributes($element, templateAttrs);
 
         if (newIsolateScopeDirective) {
           var LOCAL_REGEXP = /^\s*([@=&])(\??)\s*(\w*)\s*$/;

test/AngularSpec.js

@@ -244,19 +244,6 @@ describe('angular', function() {
       expect(clone.$some).toBe(original.$some);
     });
 
-    it('should omit properties from prototype chain', function() {
-      var original, clone = {};
-      function Func() {}
-      Func.prototype.hello = "world";
-
-      original = new Func();
-      original.goodbye = "world";
-
-      expect(shallowCopy(original, clone)).toBe(clone);
-      expect(clone.hello).toBeUndefined();
-      expect(clone.goodbye).toBe("world");
-    });
-
     it('should handle arrays', function() {
       var original = [{}, 1],
           clone = [];