perf($resource): use shallow copy instead of angular.copy

Replace calls to angular.copy with calls to a new function, shallowClearAndCopy.
Add calls to copy for cache access in $http in order to prevent modification of cached data.
Results in a measurable improvement to the startup time of complex apps within Google.

Closes #5300

src/ngResource/resource.js

@@ -24,6 +24,25 @@ function lookupDottedPath(obj, path) {
   return obj;
 }
 
+/**
+ * Create a shallow copy of an object and clear other fields from the destination
+ */
+function shallowClearAndCopy(src, dst) {
+  dst = dst || {};
+
+  angular.forEach(dst, function(value, key){
+    delete dst[key];
+  });
+
+  for (var key in src) {
+    if (src.hasOwnProperty(key) && key.substr(0, 2) !== '$$') {
+      dst[key] = src[key];
+    }
+  }
+
+  return dst;
+}
+
 /**
  * @ngdoc overview
  * @name ngResource
@@ -393,7 +412,7 @@ angular.module('ngResource', ['ng']).
       }
 
       function Resource(value){
-        copy(value || {}, this);
+        shallowClearAndCopy(value || {}, this);
       }
 
       forEach(actions, function(action, name) {
@@ -465,7 +484,7 @@ angular.module('ngResource', ['ng']).
             if (data) {
               // Need to convert action.isArray to boolean in case it is undefined
               // jshint -W018
-              if ( angular.isArray(data) !== (!!action.isArray) ) {
+              if (angular.isArray(data) !== (!!action.isArray)) {
                 throw $resourceMinErr('badcfg', 'Error in resource configuration. Expected ' +
                   'response to contain an {0} but got an {1}',
                   action.isArray?'array':'object', angular.isArray(data)?'array':'object');
@@ -477,7 +496,7 @@ angular.module('ngResource', ['ng']).
                   value.push(new Resource(item));
                 });
               } else {
-                copy(data, value);
+                shallowClearAndCopy(data, value);
                 value.$promise = promise;
               }
             }