Add support for enabling DCHECKs in release mode

src/string-stream.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_STRING_STREAM_H_
 #define V8_STRING_STREAM_H_
 
 #include "src/handles.h"
 
 namespace v8 {
@@ skipping 115 matching lines @@
 
   // Reset the stream.
   void Reset() {
     length_ = 0;
     buffer_[0] = 0;
   }
 
   // Mentioned object cache support.
   void PrintMentionedObjectCache(Isolate* isolate);
   static void ClearMentionedObjectCache(Isolate* isolate);
-#ifdef DEBUG
+#if DCHECK_IS_ON
   static bool IsMentionedObjectCacheClear(Isolate* isolate);
 #endif
 
   static const int kInitialCapacity = 16;
 
  private:
   void PrintObject(Object* obj);
 
   StringAllocator* allocator_;
   unsigned capacity_;
   unsigned length_;  // does not include terminating 0-character
   char* buffer_;
 
   bool full() const { return (capacity_ - length_) == 1; }
   int space() const { return capacity_ - length_; }
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(StringStream);
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_STRING_STREAM_H_