Adds DisplayErrorDialog to show the error message of the failure of mirroring to the users.

chromeos/display/output_configurator.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 "chromeos/display/output_configurator.h"
 
 #include <X11/Xlib.h>
 #include <X11/extensions/dpms.h>
 #include <X11/extensions/Xrandr.h>
 
@@ skipping 722 matching lines @@
 
   return success;
 }
 
 bool OutputConfigurator::SetDisplayMode(OutputState new_state) {
   if (output_state_ == STATE_INVALID ||
       output_state_ == STATE_HEADLESS ||
       output_state_ == STATE_SINGLE)
     return false;
 
-  if (output_state_ == new_state)
-    return true;
-
   Display* display = base::MessagePumpAuraX11::GetDefaultXDisplay();
   CHECK(display != NULL);
   XGrabServer(display);
   Window window = DefaultRootWindow(display);
   XRRScreenResources* screen = GetScreenResourcesAndRecordUMA(display, window);
   CHECK(screen != NULL);
 
   bool did_change = false;
   OutputSnapshot outputs[2] = { {0}, {0} };
   connected_output_count_ =
@@ skipping 100 matching lines @@
   // distinguish internal display.
   return false;
 }
 
 void OutputConfigurator::NotifyOnDisplayChanged() {
   notification_timer_.reset();
   FOR_EACH_OBSERVER(Observer, observers_, OnDisplayModeChanged());
 }
 
 }  // namespace chromeos