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

Source/core/workers/DedicatedWorkerThread.cpp

Index: Source/core/workers/DedicatedWorkerThread.cpp
diff --git a/Source/core/workers/DedicatedWorkerThread.cpp b/Source/core/workers/DedicatedWorkerThread.cpp
index 1567ddae3959d8e776c248f24f642644a0ffae52..130b9b6f5c04c5dbc5c221bc3256555eaffcda45 100644
--- a/Source/core/workers/DedicatedWorkerThread.cpp
+++ b/Source/core/workers/DedicatedWorkerThread.cpp
@@ -66,6 +66,15 @@ WebThreadSupportingGC& DedicatedWorkerThread::backingThread()
     return *m_thread.get();
 }
 
+OwnPtr<WorkerV8Isolate>& DedicatedWorkerThread::workerIsolate()
+{
+    if (!m_isolate) {
+        ASSERT(isCurrentThread());
+        m_isolate = WorkerV8Isolate::createDefault();
+    }
+    return m_isolate;
+}
+
 void DedicatedWorkerThread::postInitialize()
 {
     // Notify the parent object of our current active state before the event