Fix presubmit error introduced by r9932.

src/heap.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 264 matching lines @@
 
 #ifdef DEBUG
 class HeapDebugUtils;
 #endif
 
 
 // A queue of objects promoted during scavenge. Each object is accompanied
 // by it's size to avoid dereferencing a map pointer for scanning.
 class PromotionQueue {
  public:
-  PromotionQueue(Heap* heap)
+  explicit PromotionQueue(Heap* heap)
       : front_(NULL),
         rear_(NULL),
         limit_(NULL),
         emergency_stack_(0),
         heap_(heap) { }
 
   void Initialize();
 
   void Destroy() {
     ASSERT(is_empty());
@@ skipping 2233 matching lines @@
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(PathTracer);
 };
 #endif  // DEBUG || LIVE_OBJECT_LIST
 
 } }  // namespace v8::internal
 
 #undef HEAP
 
 #endif  // V8_HEAP_H_