Track ascii-ness of data in externalized strings.

src/execution.h

Index: src/execution.h
diff --git a/src/execution.h b/src/execution.h
index e683e122592300af3598dfda6b9d8f73527e1173..282350332ac92ff95aeec543abb60ed6b916c823 100644
--- a/src/execution.h
+++ b/src/execution.h
@@ -316,10 +316,21 @@ class GCExtension : public v8::Extension {
       v8::Handle<v8::String> name);
   static v8::Handle<v8::Value> GC(const v8::Arguments& args);
  private:
-  static const char* kSource;
+  static const char* const kSource;
 };
 
 
+class ExternalizeStringExtension : public v8::Extension {
+ public:
+  ExternalizeStringExtension() : v8::Extension("v8/externalize", kSource) {}
+  virtual v8::Handle<v8::FunctionTemplate> GetNativeFunction(
+      v8::Handle<v8::String> name);
+  static v8::Handle<v8::Value> Externalize(const v8::Arguments& args);
+  static v8::Handle<v8::Value> IsAscii(const v8::Arguments& args);
+ private:
+  static const char* const kSource;
+};
+
 } }  // namespace v8::internal
 
 #endif  // V8_EXECUTION_H_