fix: Promise.toString() to look like native function

Author: mhevery

Diff for: lib/zone.ts

@@ -1151,6 +1151,10 @@ const Zone: ZoneType = (function(global: any) {
   }
 
   class ZoneAwarePromise<R> implements Promise<R> {
+    static toString() {
+      return 'function ZoneAwarePromise() { [native code] }';
+    }
+
     static resolve<R>(value: R): Promise<R> {
       return resolvePromise(<ZoneAwarePromise<R>>new this(null), RESOLVED, value);
     }

Diff for: test/common/Promise.spec.ts

@@ -55,6 +55,10 @@ describe(
         log = [];
       });
 
+      it('should pretend to be a native code', () => {
+        expect(String(Promise).indexOf('[native code]') >= 0).toBe(true);
+      });
+
       it('should make sure that new Promise is instance of Promise', () => {
         expect(Promise.resolve(123) instanceof Promise).toBe(true);
         expect(new Promise(() => null) instanceof Promise).toBe(true);