Fix compilation with debuggersupport=off.

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 48 matching lines @@
 #include "v8utils.h"
 #include "flags.h"
 
 // Objects & heap
 #include "objects-inl.h"
 #include "spaces-inl.h"
 #include "heap-inl.h"
 #include "log-inl.h"
 #include "cpu-profiler-inl.h"
 #include "handles-inl.h"
+#include "isolate-inl.h"
 
 namespace v8 {
 namespace internal {
 
 class Deserializer;
 
 class V8 : public AllStatic {
  public:
   // Global actions.
 
@@ skipping 42 matching lines @@
   static bool has_been_disposed_;
   // True if we are using the crankshaft optimizing compiler.
   static bool use_crankshaft_;
 };
 
 } }  // namespace v8::internal
 
 namespace i = v8::internal;
 
 #endif  // V8_V8_H_