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

src/handles.h

Index: src/handles.h
diff --git a/src/handles.h b/src/handles.h
index 7eaf4de92736d3304cd80ef72fcb11fa9335a8da..f2952dfd430b3d6b73f2490bc5ffff05a26516db 100644
--- a/src/handles.h
+++ b/src/handles.h
@@ -380,6 +380,18 @@ class NoHandleAllocation BASE_EMBEDDED {
 #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_