Hold global GC heap lock while making audio thread access.

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

Index: third_party/WebKit/Source/modules/webaudio/OfflineAudioDestinationNode.cpp
diff --git a/third_party/WebKit/Source/modules/webaudio/OfflineAudioDestinationNode.cpp b/third_party/WebKit/Source/modules/webaudio/OfflineAudioDestinationNode.cpp
index 32f1f5f2a9dd8b5195da38fbe02b435007eaf7aa..e15549cfc9453e021b4c8eab71a605d00e807af4 100644
--- a/third_party/WebKit/Source/modules/webaudio/OfflineAudioDestinationNode.cpp
+++ b/third_party/WebKit/Source/modules/webaudio/OfflineAudioDestinationNode.cpp
@@ -173,7 +173,23 @@ void OfflineAudioDestinationHandler::StartOfflineRendering() {
 void OfflineAudioDestinationHandler::DoOfflineRendering() {
   DCHECK(!IsMainThread());
 
-  unsigned number_of_channels = render_target_->numberOfChannels();
+  unsigned number_of_channels;
+  Vector<float*> destinations;
+  {
+    // Main thread GCs cannot happen while we're reading out channel
+    // data. Detect that condition by trying to take the cross-thread
+    // persistent lock which is held while a GC runs. If the lock is
+    // already held, simply delay rendering until the next quantum.
+    CrossThreadPersistentRegion::LockScope gc_lock(
+        ProcessHeap::GetCrossThreadPersistentRegion(), true);
+    if (!gc_lock.HasLock())
+      return;
+
+    number_of_channels = render_target_->numberOfChannels();
+    destinations.ReserveInitialCapacity(number_of_channels);
+    for (unsigned i = 0; i < number_of_channels; ++i)
+      destinations.push_back(render_target_->getChannelData(i).View()->Data());
+  }
 
   // Reset the suspend flag.
   should_suspend_ = false;
@@ -198,9 +214,7 @@ void OfflineAudioDestinationHandler::DoOfflineRendering() {
     for (unsigned channel_index = 0; channel_index < number_of_channels;
          ++channel_index) {
       const float* source = render_bus_->Channel(channel_index)->Data();
-      float* destination =
-          render_target_->getChannelData(channel_index).View()->Data();
-      memcpy(destination + frames_processed_, source,
+      memcpy(destinations[channel_index] + frames_processed_, source,
              sizeof(float) * frames_available_to_copy);
     }