Add check to external string resource.

include/v8.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 2521 matching lines @@
 };
 
 /**
  * Ignore
  */
 class V8EXPORT Extension {  // NOLINT
  public:
   // Note that the strings passed into this constructor must live as long
   // as the Extension itself.
   Extension(const char* name,
-            const char* source = 0,
+            const char* source,
             int dep_count = 0,
             const char** deps = 0,
             int source_length = -1);
   virtual ~Extension() { }
   virtual v8::Handle<v8::FunctionTemplate>
       GetNativeFunction(v8::Handle<v8::String> name) {
     return v8::Handle<v8::FunctionTemplate>();
   }
 
   const char* name() const { return name_; }
@@ skipping 1983 matching lines @@
 
 
 }  // namespace v8
 
 
 #undef V8EXPORT
 #undef TYPE_CHECK
 
 
 #endif  // V8_H_