mus: Fix handled status in UI event ack, add MessageLoop::NestingObserver

base/run_loop.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/run_loop.h"
 
 #include "base/bind.h"
 #include "base/tracked_objects.h"
 #include "build/build_config.h"
 
@@ skipping 50 matching lines @@
 
   // Allow Quit to be called before Run.
   if (quit_called_)
     return false;
 
   // Push RunLoop stack:
   previous_run_loop_ = loop_->run_loop_;
   run_depth_ = previous_run_loop_? previous_run_loop_->run_depth_ + 1 : 1;
   loop_->run_loop_ = this;
 
+  if (run_depth_ > 1)
+    loop_->NotifyBeginNestedLoop();
+
   running_ = true;
   return true;
 }
 
 void RunLoop::AfterRun() {
   running_ = false;
 
   // Pop RunLoop stack:
   loop_->run_loop_ = previous_run_loop_;
 
   // Execute deferred QuitNow, if any:
   if (previous_run_loop_ && previous_run_loop_->quit_called_)
     loop_->QuitNow();
 }
 
 }  // namespace base