fix(zone): consistent access to __symbol__ to work with closure

We used to access Zone.__symbol__ and other times Zone[‘__symbol__’]. 
This confuses closure as it inconsistently renames symbols which breaks
code.

Author: mhevery

Diff for: lib/browser/webapis-media-query.ts

@@ -14,7 +14,7 @@
       return;
     }
     const patchEventTargetMethods =
-        (Zone as any)[(Zone as any)['__symbol__']('patchEventTargetMethods')];
+        (Zone as any)[(Zone as any).__symbol__('patchEventTargetMethods')];
     patchEventTargetMethods(
         _global['MediaQueryList'].prototype, 'addListener', 'removeListener',
         (self: any, args: any[]) => {

Diff for: lib/browser/webapis-notification.ts

@@ -18,7 +18,7 @@
     if (!desc || !desc.configurable) {
       return;
     }
-    const patchOnProperties = (Zone as any)[(Zone as any)['__symbol__']('patchOnProperties')];
+    const patchOnProperties = (Zone as any)[(Zone as any).__symbol__('patchOnProperties')];
     patchOnProperties(Notification.prototype, null);
   }
 })(typeof window === 'object' && window || typeof self === 'object' && self || global);

Diff for: lib/extra/bluebird.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 ((_global: any) => {
-  const __symbol__ = (Zone as any)['__symbol__'];
+  const __symbol__ = (Zone as any).__symbol__;
   // TODO: @JiaLiPassion, we can automatically patch bluebird
   // if global.Promise = Bluebird, but sometimes in nodejs,
   // global.Promise is not Bluebird, and Bluebird is just be

Diff for: lib/zone-spec/fake-async-test.ts

@@ -86,7 +86,7 @@
     private _microtasks: Function[] = [];
     private _lastError: Error = null;
     private _uncaughtPromiseErrors: {rejection: any}[] =
-        (Promise as any)[(Zone as any)['__symbol__']('uncaughtPromiseErrors')];
+        (Promise as any)[(Zone as any).__symbol__('uncaughtPromiseErrors')];
 
     pendingPeriodicTimers: number[] = [];
     pendingTimers: number[] = [];

Diff for: lib/zone-spec/long-stack-trace.ts

@@ -83,7 +83,7 @@ function renderLongStackTrace(frames: LongStackTrace[], stack: string): string {
     if (!error) {
       return undefined;
     }
-    const task = (error as any)[(Zone as any)['__symbol__']('currentTask')];
+    const task = (error as any)[(Zone as any).__symbol__('currentTask')];
     const trace = task && task.data && task.data[creationTrace];
     if (!trace) {
       return error.stack;

Diff for: test/browser/element.spec.ts

@@ -92,7 +92,7 @@ describe('element', function() {
      * For now we are choosing to ignore it and assume that this arrises in tests only.
      * As an added measure we make sure that all jasmine tests always run in a task. See: jasmine.ts
      */
-    global[(Zone as any)['__symbol__']('setTimeout')](() => {
+    global[(Zone as any).__symbol__('setTimeout')](() => {
       let log = '';
       button.addEventListener('click', () => {
         Zone.current.scheduleMicroTask('test', () => log += 'microtask;');

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

@@ -159,7 +159,7 @@ describe('ZoneAwareError', () => {
 
   it('should copy customized NativeError properties to ZoneAwareError', () => {
     const spy = jasmine.createSpy('errorCustomFunction');
-    const NativeError = (global as any)[(Zone as any)['__symbol__']('Error')];
+    const NativeError = (global as any)[(Zone as any).__symbol__('Error')];
     NativeError.customFunction = function(args: any) {
       spy(args);
     };

Diff for: test/extra/bluebird.spec.ts

@@ -16,7 +16,7 @@ describe('bluebird promise', () => {
     BluebirdPromise = require('bluebird');
     // import bluebird patch
     require('../../lib/extra/bluebird');
-    const patchBluebird = (Zone as any)[(Zone as any)['__symbol__']('bluebird')];
+    const patchBluebird = (Zone as any)[(Zone as any).__symbol__('bluebird')];
     patchBluebird(BluebirdPromise);
   });
 

Diff for: test/main.ts

@@ -17,7 +17,7 @@ __karma__.loaded = function() {};
 
 System.config({defaultJSExtensions: true});
 let browserPatchedPromise = null;
-if ((window as any)[(Zone as any)['__symbol__']('setTimeout')]) {
+if ((window as any)[(Zone as any).__symbol__('setTimeout')]) {
   browserPatchedPromise = Promise.resolve('browserPatched');
 } else {
   // this means that Zone has not patched the browser yet, which means we must be running in