Optimize functions on a second thread.

src/heap.h

Index: src/heap.h
diff --git a/src/heap.h b/src/heap.h
index 64fd17d61bf81332ee41a6e47dadbf3cb47db1f4..5a5470ff52aa4422507e9924a166d3c139780670 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -1620,6 +1620,25 @@ class Heap {
 
   void CheckpointObjectStats();
 
+  // We don't use a ScopedLock here since we want to lock the heap
+  // only when FLAG_parallel_recompilation is true.
+  class RelocationLock {
+   public:
+    explicit RelocationLock(Heap* heap) : heap_(heap) {
+      if (FLAG_parallel_recompilation) {
+        heap_->relocation_mutex_->Lock();
+      }
+    }
+    ~RelocationLock() {
+      if (FLAG_parallel_recompilation) {
+        heap_->relocation_mutex_->Unlock();
+      }
+    }
+
+   private:
+    Heap* heap_;
+  };
+
  private:
   Heap();
 
@@ -2072,6 +2091,8 @@ class Heap {
 
   MemoryChunk* chunks_queued_for_free_;
 
+  Mutex* relocation_mutex_;
+
   friend class Factory;
   friend class GCTracer;
   friend class DisallowAllocationFailure;