Fix a use of native JS code to avoid substituting lvalues with '#'.

sdk/lib/_internal/compiler/implementation/lib/isolate_patch.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // Patch file for the dart:isolate library.
 
 import 'dart:uri';
 
 /**
  * Called by the compiler to support switching
@@ skipping 170 matching lines @@
     topEventLoop = new _EventLoop();
     isolates = new Map<int, _IsolateContext>();
     managers = new Map<int, _ManagerStub>();
     if (isWorker) {  // "if we are not the main manager ourself" is the intent.
       mainManager = new _MainManagerStub();
       _nativeInitWorkerMessageHandler();
     }
   }
 
   void _nativeDetectEnvironment() {
-    JS("void", r"#.isWorker = $isWorker", this);
-    JS("void", r"#.supportsWorkers = $supportsWorkers", this);
-    JS("void", r"#.fromCommandLine = typeof(window) == 'undefined'", this);
+    isWorker = JS("bool", r"$isWorker");
+    supportsWorkers = JS("bool", r"$supportsWorkers");
+    fromCommandLine = JS("bool", r"typeof(window) == 'undefined'");
   }
 
   void _nativeInitWorkerMessageHandler() {
     JS("void", r"""
 $globalThis.onmessage = function (e) {
   _IsolateNatives._processWorkerMessage(this.mainManager, e);
 }""");
   }
   /*: TODO: check that _processWorkerMessage is not discarded while treeshaking.
   """ {
@@ skipping 1077 matching lines @@
       _window.clearTimeout(_handle);
     } else {
       _window.clearInterval(_handle);
     }
   }
 }
 
 Timer _timerFactory(int millis, void callback(Timer timer), bool repeating) =>
   repeating ? new _Timer.repeating(millis, callback)
             : new _Timer(millis, callback);