Remove several grab-bag includes from the v8.h header.

src/extensions/gc-extension.h

 // Copyright 2010 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_EXTENSIONS_GC_EXTENSION_H_
 #define V8_EXTENSIONS_GC_EXTENSION_H_
 
-#include "src/v8.h"
+#include "include/v8.h"
+#include "src/utils.h"
 
 namespace v8 {
 namespace internal {
 
 class GCExtension : public v8::Extension {
  public:
   explicit GCExtension(const char* fun_name)
       : v8::Extension("v8/gc",
                       BuildSource(buffer_, sizeof(buffer_), fun_name)) {}
   virtual v8::Local<v8::FunctionTemplate> GetNativeFunctionTemplate(
       v8::Isolate* isolate, v8::Local<v8::String> name);
   static void GC(const v8::FunctionCallbackInfo<v8::Value>& args);
 
  private:
   static const char* BuildSource(char* buf, size_t size, const char* fun_name) {
     SNPrintF(Vector<char>(buf, static_cast<int>(size)),
              "native function %s();", fun_name);
     return buf;
   }
 
   char buffer_[50];
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_EXTENSIONS_GC_EXTENSION_H_