Add Isolate.current getter, returning the current isolate as an Isolate object.

sdk/lib/_internal/compiler/js_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:_js_helper' show patch;
 import 'dart:_isolate_helper' show CapabilityImpl,
                                    CloseToken,
                                    IsolateNatives,
                                    JsIsolateSink,
                                    ReceivePortImpl,
                                    RawReceivePortImpl;
 
 @patch
 class Isolate {
+  static final _currentIsolateCache = IsolateNatives.currentIsolate;
+
+  // `current` must be a getter, not just a final field,
+  // to match the external declaration.
+  @patch
+  static Isolate get current => _currentIsolateCache;
+
   @patch
   static Future<Isolate> spawn(void entryPoint(message), var message,
                                      { bool paused: false }) {
     try {
       return IsolateNatives.spawnFunction(entryPoint, message, paused)
           .then((msg) => new Isolate(msg[1],
                                      pauseCapability: msg[2],
                                      terminateCapability: msg[3]));
     } catch (e, st) {
       return new Future<Isolate>.error(e, st);
@@ skipping 117 matching lines @@
   factory RawReceivePort([void handler(event)]) {
     return new RawReceivePortImpl(handler);
   }
 }
 
 @patch
 class Capability {
   @patch
   factory Capability() = CapabilityImpl;
 }