Use utils.forEach everywhere rather than Array.prototype.forEach to guard

chrome/renderer/resources/extensions/utils.js

Index: chrome/renderer/resources/extensions/utils.js
diff --git a/chrome/renderer/resources/extensions/utils.js b/chrome/renderer/resources/extensions/utils.js
index ed35e15f9fcf11e06d2a2a5792ff35c4a580d03a..50134eadb569f2b40a5ebb3c6f033eae1b1efa28 100644
--- a/chrome/renderer/resources/extensions/utils.js
+++ b/chrome/renderer/resources/extensions/utils.js
@@ -4,10 +4,20 @@
 
 var chrome = requireNative('chrome').GetChrome();
 
-function forEach(dict, f) {
-  for (var key in dict) {
-    if (dict.hasOwnProperty(key))
-      f(key, dict[key]);
+function forEach(obj, f, self) {
+  // For arrays, make sure the indices are numbers not strings - and in that
+  // case this method can be more efficient by assuming the array isn't sparse.
+  //
+  // Note: not (instanceof Array) because the array might come from a different
+  // context than our own.
+  if (obj.constructor && obj.constructor.name == 'Array') {
+    for (var i = 0; i < obj.length; i++)
+      f.call(self, i, obj[i]);
+  } else {
+    for (var key in obj) {
+      if (obj.hasOwnProperty(key))
+        f.call(self, key, obj[key]);
+    }
   }
 }