refactor(test_lib): remove IS_NODEJS

Closes #1015

modules/angular2/src/facade/lang.dart

@@ -24,6 +24,7 @@ class IMPLEMENTS {
 bool isPresent(obj) => obj != null;
 bool isBlank(obj) => obj == null;
 bool isString(obj) => obj is String;
+bool isFunction(obj) => obj is Function;
 
 String stringify(obj) => obj.toString();
 

modules/angular2/src/facade/lang.es6

@@ -38,6 +38,10 @@ export function isString(obj):boolean {
   return typeof obj === "string";
 }
 
+export function isFunction(obj):boolean {
+  return typeof obj === "function";
+}
+
 export function stringify(token):string {
   if (typeof token === 'string') {
     return token;