Added ability to lock strings to prevent their representation or encoding from changing.

src/handles.h

 // Copyright 2011 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 362 matching lines @@
   NoHandleAllocation() {}
   ~NoHandleAllocation() {}
 #else
   inline NoHandleAllocation();
   inline ~NoHandleAllocation();
  private:
   int level_;
 #endif
 };
 
+
+void LockString(Handle<String> string);
+
+// Scoped lock on a string.
+class StringLock {
+ public:
+  explicit StringLock(Handle<String> string);
+  ~StringLock();
+ private:
+  Handle<String> string_;
+};
+
 } }  // namespace v8::internal
 
 #endif  // V8_HANDLES_H_