compositor-worker: Initialize CW machinery plumbing to compositor and fire CW rAF callbacks.

third_party/WebKit/Source/modules/compositorworker/CompositorWorkerThread.cpp

Index: third_party/WebKit/Source/modules/compositorworker/CompositorWorkerThread.cpp
diff --git a/third_party/WebKit/Source/modules/compositorworker/CompositorWorkerThread.cpp b/third_party/WebKit/Source/modules/compositorworker/CompositorWorkerThread.cpp
index 78f1ed6beb27b0a324c26fab5deda377eb353b22..349a8055f594ff127f46a44f6182fd3f9ef36760 100644
--- a/third_party/WebKit/Source/modules/compositorworker/CompositorWorkerThread.cpp
+++ b/third_party/WebKit/Source/modules/compositorworker/CompositorWorkerThread.cpp
@@ -33,6 +33,7 @@ public:
     }
 
     WorkerBackingThread* thread() { return m_thread.get(); }
+    void clear() { m_thread = nullptr; }
     void resetForTest()
     {
         ASSERT(!m_thread || (m_thread->workerScriptCount() == 0));
@@ -77,6 +78,16 @@ WorkerGlobalScope*CompositorWorkerThread::createWorkerGlobalScope(PassOwnPtr<Wor
     return CompositorWorkerGlobalScope::create(this, std::move(startupData), m_timeOrigin);
 }
 
+void CompositorWorkerThread::ensureSharedBackingThread()
+{
+    BackingThreadHolder::instance();
+}
+
+void CompositorWorkerThread::clearSharedBackingThread()
+{
+    BackingThreadHolder::instance().clear();
+}
+
 void CompositorWorkerThread::resetSharedBackingThreadForTest()
 {
     BackingThreadHolder::instance().resetForTest();