Hold global GC heap lock while making audio thread access.

third_party/WebKit/Source/platform/heap/ThreadState.cpp

Index: third_party/WebKit/Source/platform/heap/ThreadState.cpp
diff --git a/third_party/WebKit/Source/platform/heap/ThreadState.cpp b/third_party/WebKit/Source/platform/heap/ThreadState.cpp
index 2c2b2630b7007c9910fcc1ae6a3226be81463c06..a8716456f3b924dcc1688d170aafe2a800546818 100644
--- a/third_party/WebKit/Source/platform/heap/ThreadState.cpp
+++ b/third_party/WebKit/Source/platform/heap/ThreadState.cpp
@@ -1453,9 +1453,11 @@ void ThreadState::CollectGarbage(BlinkGC::StackState stack_state,
   GCForbiddenScope gc_forbidden_scope(this);
 
   {
-    // Access to the CrossThreadPersistentRegion has to be prevented while in
-    // the marking phase because otherwise other threads may allocate or free
-    // PersistentNodes and we can't handle that.
+    // Access to the CrossThreadPersistentRegion has to be prevented
+    // while in the marking phase because otherwise other threads may
+    // allocate or free PersistentNodes and we can't handle
+    // that. Grabbing this lock also prevents non-attached threads
+    // from accessing any GCed heap while a GC runs.
     CrossThreadPersistentRegion::LockScope persistent_lock(
         ProcessHeap::GetCrossThreadPersistentRegion());
     {