Remove Sync JS generic request/reply framework

sync/js/js_backend.h

Index: sync/js/js_backend.h
diff --git a/sync/js/js_backend.h b/sync/js/js_backend.h
index e39600a8bcb9750f82fb51e96039379e233938d0..a0ef317ba6f77f04dd98364560ce4f8202235059 100644
--- a/sync/js/js_backend.h
+++ b/sync/js/js_backend.h
@@ -13,9 +13,7 @@
 
 namespace syncer {
 
-class JsArgList;
 class JsEventHandler;
-class JsReplyHandler;
 template <typename T> class WeakHandle;
 
 // Interface representing the backend of chrome://sync-internals.  A
@@ -27,12 +25,6 @@ class SYNC_EXPORT_PRIVATE JsBackend {
   virtual void SetJsEventHandler(
       const WeakHandle<JsEventHandler>& event_handler) = 0;
 
-  // Processes the given message and replies via the given handler, if
-  // initialized.
-  virtual void ProcessJsMessage(
-      const std::string& name, const JsArgList& args,
-      const WeakHandle<JsReplyHandler>& reply_handler) = 0;
-
  protected:
   virtual ~JsBackend() {}
 };