compositor-worker: Share a thread and an isolate for compositor workers.

Source/core/workers/WorkerThreadTest.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "core/workers/WorkerThread.h"
 
 #include "core/inspector/ConsoleMessage.h"
 #include "core/workers/WorkerReportingProxy.h"
 #include "core/workers/WorkerThreadStartupData.h"
@@ skipping 79 matching lines @@
     }
 
     ~WorkerThreadForTest() override { }
 
     // WorkerThread implementation:
     WebThreadSupportingGC& backingThread() override
     {
         return *m_thread;
     }
 
+    OwnPtr<WorkerV8Isolate>& workerIsolate() override
+    {
+        if (!m_isolate) {
+            ASSERT(isCurrentThread());
+            m_isolate = WorkerV8Isolate::createDefault();
+        }
+        return m_isolate;
+    }
+
     MOCK_METHOD1(doIdleGc, bool(double deadlineSeconds));
 
     PassRefPtrWillBeRawPtr<WorkerGlobalScope> createWorkerGlobalScope(PassOwnPtr<WorkerThreadStartupData> startupData) override
     {
         return adoptRefWillBeNoop(new FakeWorkerGlobalScope(startupData->m_scriptURL, startupData->m_userAgent, this, startupData->m_starterOrigin, startupData->m_workerClients.release()));
     }
 
 private:
     OwnPtr<WebThreadSupportingGC> m_thread;
+    OwnPtr<WorkerV8Isolate> m_isolate;
 };
 
 class WakeupTask : public WebThread::Task {
 public:
     WakeupTask() { }
 
     ~WakeupTask() override { }
 
     void run() override { }
 };
@@ skipping 168 matching lines @@
 
     completion->wait();
 
     // Make sure doIdleGc has not been called by this stage.
     Mock::VerifyAndClearExpectations(m_workerThread.get());
 
     m_workerThread->terminateAndWait();
 }
 
 } // namespace blink