Simple BlinkGC heap compaction.

third_party/WebKit/Source/wtf/Deque.h

Index: third_party/WebKit/Source/wtf/Deque.h
diff --git a/third_party/WebKit/Source/wtf/Deque.h b/third_party/WebKit/Source/wtf/Deque.h
index ac5a6d085a782dc2b441a36563e89e876d4f3be3..45b475aaad98066b3cc3e214538ea279a696cb18 100644
--- a/third_party/WebKit/Source/wtf/Deque.h
+++ b/third_party/WebKit/Source/wtf/Deque.h
@@ -656,8 +656,10 @@ void Deque<T, inlineCapacity, Allocator>::trace(VisitorDispatcher visitor) {
             visitor, *const_cast<T*>(bufferEntry));
     }
   }
-  if (m_buffer.hasOutOfLineBuffer())
+  if (m_buffer.hasOutOfLineBuffer()) {
     Allocator::markNoTracing(visitor, m_buffer.buffer());
+    Allocator::registerBackingStoreReference(visitor, m_buffer.bufferSlot());
+  }
 }
 
 template <typename T, size_t inlineCapacity, typename Allocator>