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

Source/modules/compositorworker/CompositorWorkerThread.cpp

Index: Source/modules/compositorworker/CompositorWorkerThread.cpp
diff --git a/Source/modules/compositorworker/CompositorWorkerThread.cpp b/Source/modules/compositorworker/CompositorWorkerThread.cpp
index fa420027933081e3485cf6dce85ce7dc3144510f..b540dd5befbdaaef56f553d9d110a4dcbc5435b0 100644
--- a/Source/modules/compositorworker/CompositorWorkerThread.cpp
+++ b/Source/modules/compositorworker/CompositorWorkerThread.cpp
@@ -9,7 +9,6 @@
 #include "core/workers/WorkerObjectProxy.h"
 #include "core/workers/WorkerThreadStartupData.h"
 #include "modules/compositorworker/CompositorWorkerGlobalScope.h"
-#include "modules/compositorworker/CompositorWorkerManager.h"
 #include "public/platform/Platform.h"
 
 namespace blink {
@@ -38,37 +37,9 @@
 
 WebThreadSupportingGC& CompositorWorkerThread::backingThread()
 {
-    return CompositorWorkerManager::instance()->compositorWorkerThread();
-}
-
-void CompositorWorkerThread::initializeBackingThread()
-{
-    CompositorWorkerManager::instance()->initializeBackingThread();
-}
-
-void CompositorWorkerThread::shutdownBackingThread()
-{
-    CompositorWorkerManager::instance()->shutdownBackingThread();
-}
-
-v8::Isolate* CompositorWorkerThread::initializeIsolate()
-{
-    return CompositorWorkerManager::instance()->initializeIsolate();
-}
-
-void CompositorWorkerThread::willDestroyIsolate()
-{
-    CompositorWorkerManager::instance()->willDestroyIsolate();
-}
-
-void CompositorWorkerThread::destroyIsolate()
-{
-    CompositorWorkerManager::instance()->destroyIsolate();
-}
-
-void CompositorWorkerThread::terminateV8Execution()
-{
-    CompositorWorkerManager::instance()->terminateV8Execution();
+    if (!m_thread)
+        m_thread = WebThreadSupportingGC::create("CompositorWorker Thread");
+    return *m_thread.get();
 }
 
 } // namespace blink