Implement suspend() and resume() for OfflineAudioContext

Source/modules/webaudio/DeferredTaskHandler.cpp

Index: Source/modules/webaudio/DeferredTaskHandler.cpp
diff --git a/Source/modules/webaudio/DeferredTaskHandler.cpp b/Source/modules/webaudio/DeferredTaskHandler.cpp
index e5ded30448748d06e92bb85998c3243ef5dc2d82..d4bde56d5a4c32c63545891493df8d4074544ede 100644
--- a/Source/modules/webaudio/DeferredTaskHandler.cpp
+++ b/Source/modules/webaudio/DeferredTaskHandler.cpp
@@ -41,6 +41,12 @@ void DeferredTaskHandler::lock()
     m_contextGraphMutex.lock();
 }
 
+void DeferredTaskHandler::offlineContextLock()
+{
+    ASSERT(!isMainThread());
+    m_contextGraphMutex.lock();
+}
+
 bool DeferredTaskHandler::tryLock()
 {
     // Try to catch cases of using try lock on main thread