Fix errors in display resolution change notifications

chrome/browser/extensions/display_info_provider_chromeos.cc

 // Copyright 2014 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 "chrome/browser/extensions/display_info_provider_chromeos.h"
 
 #include <stdint.h>
 
 #include "ash/common/wm/maximize_mode/maximize_mode_controller.h"
 #include "ash/display/display_configuration_controller.h"
@@ skipping 324 matching lines @@
         new display::ManagedDisplayMode(
             size, current_mode->refresh_rate(), current_mode->is_interlaced(),
             info.display_mode->is_native, info.display_mode->ui_scale,
             info.display_mode->device_scale_factor));
 
     if (new_mode->IsEquivalent(current_mode)) {
       *error = "Display mode matches current mode.";
       return false;
     }
 
-    if (!display_manager->SetDisplayMode(id, new_mode)) {
-      *error = "Unable to set the display mode.";
-      return false;
-    }
-
+    // We must prepare the notification before we set the mode, since setting
+    // the mode actually shows the notification, so it should be ready by then.
+    // crbug.com/701389.

[stevenjb, 2017/04/06 22:10:53]

This is all kind of awkward. It looks like we do this here because
DisplayManager doesn't have access to resolution_notification_controller?

Can we explain what all is going on here, e.g (I may have this wrong):
* We prepare an Ash notification here.
* If DisplayManager successfully sets the new display mode, it triggers the
actual notification (where?)
* If the user confirms the change (?) the notification calls StoreDisplayPrefs ?

[afakhry, 2017/04/07 00:04:57]

ResolutionNotificationController::OnDisplayConfigurationChanged()
Yes, in ResolutionNotificationController::AcceptResolutionChange().

This should be documented in the doc for
ResolutionNotificationController::PrepareNotification() here:
https://cs.chromium.org/chromium/src/ash/display/resolution_notification_cont...

So in order to avoid repetition of docs, please let me know what's the degree of
details you want to include here.

     if (!display::Display::IsInternalDisplayId(id)) {
       // For external displays, show a notification confirming the resolution
       // change.
       ash::Shell::GetInstance()
           ->resolution_notification_controller()
           ->PrepareNotification(id, current_mode, new_mode,
                                 base::Bind(&chromeos::StoreDisplayPrefs));
     }
+
+    if (!display_manager->SetDisplayMode(id, new_mode)) {
+      *error = "Unable to set the display mode.";
+      return false;
+    }
   }
   return true;
 }
 
 system_display::DisplayMode GetDisplayMode(
     display::DisplayManager* display_manager,
     const display::ManagedDisplayInfo& display_info,
     const scoped_refptr<display::ManagedDisplayMode>& display_mode) {
   system_display::DisplayMode result;
 
@@ skipping 528 matching lines @@
     touch_calibrator_.reset(new chromeos::TouchCalibratorController);
   return touch_calibrator_.get();
 }
 
 // static
 DisplayInfoProvider* DisplayInfoProvider::Create() {
   return new DisplayInfoProviderChromeOS();
 }
 
 }  // namespace extensions