fix(zone.js): handle fetch with AbortSignal

fetch support AbortSignal, zone.js schedules a macroTask when fetch()

```
fetch(..., {signal: abortSignal});
```

we should also be able to cancel fetch with `zoneTask.cancel` call.
So this commit create an internal AbortSignal to handle
`zoneTask.cancel()` call and also delegate the `options.signal` from the
user code.

packages/zone.js/lib/common/fetch.ts

@@ -26,15 +26,22 @@ Zone.__load_patch('fetch', (global: any, Zone: ZoneType, api: _ZonePrivate) => {
   const ZoneAwarePromise = global.Promise;
   const symbolThenPatched = api.symbol('thenPatched');
   const fetchTaskScheduling = api.symbol('fetchTaskScheduling');
-  const fetchTaskAborting = api.symbol('fetchTaskAborting');
-  const OriginalAbortController = global['AbortController'];
-  const supportAbort = typeof OriginalAbortController === 'function';
-  let abortNative: Function|null = OriginalAbortController?.prototype[api.symbol('abort')];
   const placeholder = function() {};
   global['fetch'] = function() {
     const args = Array.prototype.slice.call(arguments);
-    const options = args.length > 1 ? args[1] : null;
+    const options = args.length > 1 ? args[1] : {};
     const signal = options && options.signal;
+    const ac = new AbortController();
+    const fetchSignal = ac.signal;
+    options.signal = fetchSignal;
+    args[1] = options;
+    if (signal) {
+      const nativeAddEventListener =
+          signal[Zone.__symbol__('addEventListener')] || signal.addEventListener;
+      nativeAddEventListener.call(signal, 'abort', function() {
+        ac!.abort();
+      });
+    }
     return new Promise((res, rej) => {
       const task = Zone.current.scheduleMacroTask(
           'fetch', placeholder, {fetchArgs: args} as FetchTaskData,
@@ -72,25 +79,8 @@ Zone.__load_patch('fetch', (global: any, Zone: ZoneType, api: _ZonePrivate) => {
                 });
           },
           () => {
-            if (!supportAbort) {
-              rej('No AbortController supported, can not cancel fetch');
-              return;
-            }
-            if (signal && signal.abortController && !signal.aborted &&
-                typeof signal.abortController.abort === 'function' && abortNative) {
-              try {
-                (Zone.current as any)[fetchTaskAborting] = true;
-                abortNative.call(signal.abortController);
-              } finally {
-                (Zone.current as any)[fetchTaskAborting] = false;
-              }
-            } else {
-              rej('cancel fetch need a AbortController.signal');
-            }
+            ac.abort();
           });
-      if (signal && signal.abortController) {
-        signal.abortController.tasks = [task];
-      }
     });
   };
 });