Update the current frame count in a safe place

Source/modules/webaudio/AudioContext.cpp

Index: Source/modules/webaudio/AudioContext.cpp
diff --git a/Source/modules/webaudio/AudioContext.cpp b/Source/modules/webaudio/AudioContext.cpp
index fde9cf2c51d36e4aea01626108c36d93ef42d011..81d06b4110e417210f3df9a393c6b9a2f833ec04 100644
--- a/Source/modules/webaudio/AudioContext.cpp
+++ b/Source/modules/webaudio/AudioContext.cpp
@@ -109,6 +109,7 @@ AudioContext::AudioContext(Document* document)
     , m_audioThread(0)
     , m_isOfflineContext(false)
     , m_contextState(Suspended)
+    , m_shadowCurrentSampleFrame(0)
 {
     m_referencedNodes = new HeapVector<Member<AudioNode>>();
     m_destinationNode = DefaultAudioDestinationNode::create(this);
@@ -132,6 +133,7 @@ AudioContext::AudioContext(Document* document, unsigned numberOfChannels, size_t
     , m_audioThread(0)
     , m_isOfflineContext(true)
     , m_contextState(Suspended)
+    , m_shadowCurrentSampleFrame(0)
 {
     m_referencedNodes = new HeapVector<Member<AudioNode>>();
     // Create a new destination for offline rendering.
@@ -553,6 +555,13 @@ PeriodicWave* AudioContext::createPeriodicWave(DOMFloat32Array* real, DOMFloat32
     return PeriodicWave::create(sampleRate(), real, imag);
 }
 
+size_t AudioContext::sampleFrame() const
+{
+    ASSERT(isMainThread());
+
+    return m_shadowCurrentSampleFrame;
+}
+
 String AudioContext::state() const
 {
     // These strings had better match the strings for AudioContextState in AudioContext.idl.
@@ -765,6 +774,9 @@ void AudioContext::handlePreRenderTasks()
         updateAutomaticPullNodes();
         resolvePromisesForResume();
 
+        // Update the shadow frame value.
+        m_shadowCurrentSampleFrame = currentSampleFrame();
+
         unlock();
     }
 }