Fix presubmit error in r11270.

src/hydrogen.h

 // Copyright 2012 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 1208 matching lines @@
   HValueMapListElement* array_;  // Primary store - contains the first value
   // with a given hash.  Colliding elements are stored in linked lists.
   HValueMapListElement* lists_;  // The linked lists containing hash collisions.
   int free_list_head_;  // Unused elements in lists_ are on the free list.
 };
 
 
 class HSideEffectMap BASE_EMBEDDED {
  public:
   HSideEffectMap();
-  HSideEffectMap(HSideEffectMap* other);
+  explicit HSideEffectMap(HSideEffectMap* other);
 
   void Kill(GVNFlagSet flags);
 
   void Store(GVNFlagSet flags, HInstruction* instr);
 
   bool IsEmpty() const { return count_ == 0; }
 
   inline HInstruction* operator[](int i) const {
     ASSERT(0 <= i);
     ASSERT(i < kNumberOfTrackedSideEffects);
@@ skipping 158 matching lines @@
   const char* filename_;
   HeapStringAllocator string_allocator_;
   StringStream trace_;
   int indent_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_H_