Revert "Implement scheduleImmediate on Chrome/Drt/Safari/Firefox."

sdk/lib/_internal/lib/async_patch.dart

Index: sdk/lib/_internal/lib/async_patch.dart
diff --git a/sdk/lib/_internal/lib/async_patch.dart b/sdk/lib/_internal/lib/async_patch.dart
index 004f433b54f36d8ebc6bc1758b8b371c9583a3e6..0203e4dabf2f50192698dbe11615de80fea08ef8 100644
--- a/sdk/lib/_internal/lib/async_patch.dart
+++ b/sdk/lib/_internal/lib/async_patch.dart
@@ -8,8 +8,7 @@ import 'dart:_js_helper' show
     patch,
     Primitives,
     convertDartClosureToJS,
-    loadDeferredLibrary,
-    requiresPreamble;
+    loadDeferredLibrary;
 import 'dart:_isolate_helper' show
     IsolateNatives,
     TimerImpl,
@@ -31,44 +30,11 @@ class _AsyncRun {
       _initializeScheduleImmediate();
 
   static Function _initializeScheduleImmediate() {
-    requiresPreamble();
     if (JS('', 'self.scheduleImmediate') != null) {
       return _scheduleImmediateJsOverride;
     }
-    if (JS('', 'self.MutationObserver') != null &&
-        JS('', 'self.document') != null) {
-      // Use mutationObservers.
-      var div = JS('', 'self.document.createElement("div")');
-      var span = JS('', 'self.document.createElement("span")');
-      var storedCallback;
-
-      internalCallback(_) {
-        leaveJsAsync();
-        var f = storedCallback;
-        storedCallback = null;
-        f();
-      };
-
-      var observer = JS('', 'new self.MutationObserver(#)',
-          convertDartClosureToJS(internalCallback, 1));
-      JS('', '#.observe(#, { childList: true })',
-          observer, div);
-
-      return (void callback()) {
-        assert(storedCallback == null);
-        enterJsAsync();
-        storedCallback = callback;
-        // Because of a broken shadow-dom polyfill we have to change the
-        // children instead a cheap property.
-        // See https://github.com/Polymer/ShadowDOM/issues/468
-        JS('', '#.firstChild ? #.removeChild(#): #.appendChild(#)',
-            div, div, span, div, span);
-      };
-
-    }
     // TODO(9002): don't use the Timer to enqueue the immediate callback.
-    // Also check for other JS options like setImmediate.
-    // TODO(20055): We should use DOM promises when available.
+    // Also check for other JS options like mutation observer or runImmediate.
     return _scheduleImmediateWithTimer;
   }