Reland of "[heap] Parallel newspace evacuation, semispace copy, and compaction \o/"

src/heap/array-buffer-tracker.cc

Index: src/heap/array-buffer-tracker.cc
diff --git a/src/heap/array-buffer-tracker.cc b/src/heap/array-buffer-tracker.cc
index bbe3c6b93679324f90eaa037bbd6e8b71bde07cf..6e389c1cbf6abe216c782bae30fedcba5b283443 100644
--- a/src/heap/array-buffer-tracker.cc
+++ b/src/heap/array-buffer-tracker.cc
@@ -77,6 +77,7 @@ void ArrayBufferTracker::Unregister(JSArrayBuffer* buffer) {
 
 
 void ArrayBufferTracker::MarkLive(JSArrayBuffer* buffer) {
+  base::LockGuard<base::Mutex> guard(&mutex_);
   void* data = buffer->backing_store();
 
   // ArrayBuffer might be in the middle of being constructed.
@@ -123,6 +124,8 @@ void ArrayBufferTracker::PrepareDiscoveryInNewSpace() {
 
 
 void ArrayBufferTracker::Promote(JSArrayBuffer* buffer) {
+  base::LockGuard<base::Mutex> guard(&mutex_);
+
   if (buffer->is_external()) return;
   void* data = buffer->backing_store();
   if (!data) return;