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

Source/core/workers/WorkerThread.h

Index: Source/core/workers/WorkerThread.h
diff --git a/Source/core/workers/WorkerThread.h b/Source/core/workers/WorkerThread.h
index 2405c86493da3a2d74d818d58207bc8e2333576c..cc969a6ae3f4835d229be567d7867bb2ef3322ca 100644
--- a/Source/core/workers/WorkerThread.h
+++ b/Source/core/workers/WorkerThread.h
@@ -31,6 +31,7 @@
 #include "core/dom/ExecutionContextTask.h"
 #include "core/frame/csp/ContentSecurityPolicy.h"
 #include "core/workers/WorkerGlobalScope.h"
+#include "core/workers/WorkerIsolateWrapper.h"
 #include "core/workers/WorkerLoaderProxy.h"
 #include "platform/WebThreadSupportingGC.h"
 #include "platform/weborigin/SecurityOrigin.h"
@@ -69,11 +70,10 @@ public:
     // some implementations can use an existing thread that is already being
     // used by other workers (e.g.  compositor workers).
     virtual WebThreadSupportingGC& backingThread() = 0;
-
     virtual void didStartRunLoop();
     virtual void didStopRunLoop();
 
-    v8::Isolate* isolate() const { return m_isolate; }
+    v8::Isolate* isolate();
 
     // Can be used to wait for this worker thread to shut down.
     // (This is signalled on the main thread, so it's assumed to be waited on the worker context thread)
@@ -122,9 +122,14 @@ protected:
 
     virtual void postInitialize() { }
 
-    virtual v8::Isolate* initializeIsolate();
-    virtual void willDestroyIsolate();
-    virtual void destroyIsolate();
+    // Both of these methods are called in the worker thread.
+    virtual void initializeBackingThread();
+    virtual void shutdownBackingThread();
+
+    // The WorkerIsolateWrapper is created in the worker thread.
+    virtual PassOwnPtr<WorkerIsolateWrapper> createIsolateWrapper();
+
+    // This is called on the main-thread.
     virtual void terminateV8Execution();
 
     // This is protected virtual for testing.
@@ -155,13 +160,11 @@ private:
     RefPtrWillBePersistent<WorkerInspectorController> m_workerInspectorController;
     Mutex m_workerInspectorControllerMutex;
 
-    // This lock protects |m_workerGlobalScope|, |m_terminated|, |m_isolate| and |m_microtaskRunner|.
+    // This lock protects |m_workerGlobalScope|, |m_terminated|, and |m_isolateWrapper|.
     Mutex m_threadStateMutex;
 
     RefPtrWillBePersistent<WorkerGlobalScope> m_workerGlobalScope;
-
-    v8::Isolate* m_isolate;
-    OwnPtr<V8IsolateInterruptor> m_interruptor;
+    OwnPtr<WorkerIsolateWrapper> m_isolateWrapper;
 
     // Used to signal thread shutdown.
     OwnPtr<WebWaitableEvent> m_shutdownEvent;