Backport the changes from the readability.

src/v8.h

 // Copyright 2006-2008 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 20 matching lines @@
 
 #ifndef V8_V8_H_
 #define V8_V8_H_
 
 #if defined(GOOGLE3)
 // Google3 special flag handling.
 #if defined(DEBUG) && defined(NDEBUG)
 // If both are defined in Google3, then we are building an optimized v8 with
 // assertions enabled.
 #undef NDEBUG
+#elif !defined(DEBUG) && !defined(NDEBUG)
+// If neither is defined in Google3, then we are building a debug v8. Mark it
+// as such.
+#define DEBUG

[Feng Qian, 2008/11/04 22:05:53]

This is a big confusing. Maybe you should explain the expected build of all 4
combination in Google3.

 #endif
 #endif  // defined(GOOGLE3)
 
 // V8 only uses DEBUG, but included external files
 // may use NDEBUG - make sure they are consistent.
 #if defined(DEBUG) && defined(NDEBUG)
 #error both DEBUG and NDEBUG are set
 #endif
 
 // Basic includes
@@ skipping 31 matching lines @@
   // Report process out of memory. Implementation found in api.cc.
   static void FatalProcessOutOfMemory(const char* location);
  private:
   static bool has_been_setup_;
   static bool has_been_disposed_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_V8_H_