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..339e3fd9b32f5cfdaa28c5529ac7bb2733935b78 100644
--- a/Source/modules/webaudio/DeferredTaskHandler.cpp
+++ b/Source/modules/webaudio/DeferredTaskHandler.cpp
@@ -41,6 +41,14 @@ void DeferredTaskHandler::lock()
     m_contextGraphMutex.lock();
 }
 
+void DeferredTaskHandler::forceLock()
+{
+    // This allows the regular lock in offline audio rendering. It is okay to

[Raymond Toy, 2015/07/15 20:59:14]

What do you mean by "allows the regular lock"?

[hongchan, 2015/07/15 23:24:22]

What I meant was this lock is not a 'tryLock()'.

[Raymond Toy, 2015/07/16 16:52:04]

Maybe it would be clearer if forceLock were named offlineContextLock or
something?

[hongchan, 2015/07/16 17:24:37]

Done.

+    // lock the offline audio render thread because it is not real-time thread.
+    ASSERT(!isMainThread());

[Raymond Toy, 2015/07/16 16:52:04]

Can we also assert that this is not the audio thread (online context)?  Or
assert that this is the offline context thread?

[hongchan, 2015/07/16 17:24:37]

This is not possible. The offline render thread is the audio thread; calling
render() sets the offline render thread to the audio thread for every render
quantum.

Also DeferredTaskHandler does not have a clue about the type of context. So we
cannot query like |isOfflineContext()| here. I think keeping them separate is
better and that's why I was hesitant to include 'offline' in the method name.

+    m_contextGraphMutex.lock();
+}
+
 bool DeferredTaskHandler::tryLock()
 {
     // Try to catch cases of using try lock on main thread