XMLHttpRequest#responseText should use a rope

Source/core/inspector/InspectorInstrumentation.idl

Index: Source/core/inspector/InspectorInstrumentation.idl
diff --git a/Source/core/inspector/InspectorInstrumentation.idl b/Source/core/inspector/InspectorInstrumentation.idl
index 3906fa99ff7bf4bd8ea6d1a8ef749efbb8430d71..a2fb2db099ed12097bea16aec686e94cf32498e8 100644
--- a/Source/core/inspector/InspectorInstrumentation.idl
+++ b/Source/core/inspector/InspectorInstrumentation.idl
@@ -291,7 +291,7 @@ interface InspectorInstrumentation {
     void didFailXHRLoading(ScriptExecutionContext*, ThreadableLoaderClient* client);
 
     [Console, Resource]
-    void didFinishXHRLoading(ScriptExecutionContext*, ThreadableLoaderClient* client, unsigned long identifier, const String& sourceString, const String& url, const String& sendURL, unsigned sendLineNumber);
+    void didFinishXHRLoading(ScriptExecutionContext*, ThreadableLoaderClient* client, unsigned long identifier, ScriptString sourceString, const String& url, const String& sendURL, unsigned sendLineNumber);
 
     [Resource]
     void didReceiveXHRResponse(ScriptExecutionContext*, unsigned long identifier);