Implement suspend() and resume() for OfflineAudioContext

Source/modules/webaudio/DeferredTaskHandler.h

Index: Source/modules/webaudio/DeferredTaskHandler.h
diff --git a/Source/modules/webaudio/DeferredTaskHandler.h b/Source/modules/webaudio/DeferredTaskHandler.h
index b145642b82ea96eb3bd9de6e5d1ab3f3de8955c8..c653ccb43fd27ab2116eee4c5d0f16c26506b731 100644
--- a/Source/modules/webaudio/DeferredTaskHandler.h
+++ b/Source/modules/webaudio/DeferredTaskHandler.h
@@ -108,8 +108,15 @@ public:
     bool isAudioThread() const { return currentThread() == acquireLoad(&m_audioThread); }
 
     void lock();
+
+    // This must be used only for OfflineAudioContext. It allows the regular
+    // lock (instead of tryLock) in offline audio rendering and it is okay to
+    // lock the offline audio render thread because it is not real-time thread.
+    void offlineContextLock();
+
     bool tryLock();
     void unlock();
+
 #if ENABLE(ASSERT)
     // Returns true if this thread owns the context's lock.
     bool isGraphOwner();