Initialize DeferredTaskHandler's audio thread ID once.

third_party/WebKit/Source/modules/webaudio/DeferredTaskHandler.cpp

Index: third_party/WebKit/Source/modules/webaudio/DeferredTaskHandler.cpp
diff --git a/third_party/WebKit/Source/modules/webaudio/DeferredTaskHandler.cpp b/third_party/WebKit/Source/modules/webaudio/DeferredTaskHandler.cpp
index b7e55de0e324a5bfb438dc4108f89d9bb1f06519..08a748884849b175b2db7d0d74e583f10c3396fd 100644
--- a/third_party/WebKit/Source/modules/webaudio/DeferredTaskHandler.cpp
+++ b/third_party/WebKit/Source/modules/webaudio/DeferredTaskHandler.cpp
@@ -279,5 +279,16 @@ void DeferredTaskHandler::clearHandlersToBeDeleted()
     m_deletableOrphanHandlers.clear();
 }
 
+void DeferredTaskHandler::setAudioThreadToCurrentThread()
+{
+    ASSERT(!isMainThread());
+    if (m_audioThread) {
+        ASSERT(m_audioThread == currentThread());
+        return;
+    }
+    ThreadIdentifier thread = currentThread();
+    releaseStore(&m_audioThread, thread);
+}
+
 } // namespace blink