perf(shallowCopy): use Object.keys to improve performance

This change is not IE8 friendly

Author: IgorMinar

src/Angular.js

@@ -819,17 +819,22 @@ function copy(source, destination, stackSource, stackDest) {
  * Creates a shallow copy of an object, an array or a primitive
  */
 function shallowCopy(src, dst) {
+  var i = 0;
   if (isArray(src)) {
     dst = dst || [];
 
-    for ( var i = 0; i < src.length; i++) {
+    for (; i < src.length; i++) {
       dst[i] = src[i];
     }
   } else if (isObject(src)) {
     dst = dst || {};
 
-    for (var key in src) {
-      if (hasOwnProperty.call(src, key) && !(key.charAt(0) === '$' && key.charAt(1) === '$')) {
+    var keys = Object.keys(src);
+
+    for (var l = keys.length; i < l; i++) {
+      var key = keys[i];
+
+      if (!(key.charAt(0) === '$' && key.charAt(1) === '$')) {
         dst[key] = src[key];
       }
     }