refactor(core): use native String.prototype.trim if available

src/Angular.js

@@ -442,9 +442,20 @@ function isBoolean(value) {
 }
 
 
-function trim(value) {
-  return isString(value) ? value.replace(/^\s*/, '').replace(/\s*$/, '') : value;
-}
+var trim = (function() {
+  // native trim is way faster: http://jsperf.com/angular-trim-test
+  // but IE doesn't have it... :-(
+  // TODO: we should move this into IE/ES5 polyfill
+  if (!String.prototype.trim) {
+    return function(value) {
+      return isString(value) ? value.replace(/^\s*/, '').replace(/\s*$/, '') : value;
+    };
+  }
+  return function(value) {
+    return isString(value) ? value.trim() : value;
+  };
+})();
+
 
 /**
  * @ngdoc function