Fix errors in display resolution change notifications

chrome/browser/ui/webui/options/chromeos/display_options_handler.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 "chrome/browser/ui/webui/options/chromeos/display_options_handler.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <memory>
@@ skipping 473 matching lines @@
 
   scoped_refptr<display::ManagedDisplayMode> mode =
       ConvertValueToManagedDisplayMode(mode_data);
   if (!mode)
     return;
 
   base::RecordAction(base::UserMetricsAction("Options_DisplaySetResolution"));
   display::DisplayManager* display_manager = GetDisplayManager();
   scoped_refptr<display::ManagedDisplayMode> current_mode =
       display_manager->GetActiveModeForDisplayId(display_id);
+
+  if (mode->IsEquivalent(current_mode)) {
+    LOG(ERROR) << "New display mode matches current mode.";
+    return;
+  }
+
+  // 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.
+  if (display::Display::IsInternalDisplayId(display_id)) {
+    // For external displays, show a notification confirming the resolution
+    // change.
+    ash::Shell::GetInstance()
+        ->resolution_notification_controller()
+        ->PrepareNotification(display_id, current_mode, mode,
+                              base::Bind(&chromeos::StoreDisplayPrefs));
+  }
+
   if (!display_manager->SetDisplayMode(display_id, mode)) {
     LOG(ERROR) << "Unable to set display mode for: " << display_id
                << " Mode: " << *mode_data;
-    return;
   }
-  if (display::Display::IsInternalDisplayId(display_id))
-    return;
-  // For external displays, show a notification confirming the resolution
-  // change.
-  ash::Shell::GetInstance()
-      ->resolution_notification_controller()
-      ->PrepareNotification(display_id, current_mode, mode,
-                            base::Bind(&chromeos::StoreDisplayPrefs));
 }
 
 void DisplayOptionsHandler::HandleSetRotation(const base::ListValue* args) {
   DCHECK(!args->empty());
 
   int64_t display_id = GetDisplayIdFromArgs(args);
   if (display_id == display::kInvalidDisplayId)
     return;
 
   int rotation_value = 0;
@@ skipping 54 matching lines @@
   if (!args->GetBoolean(0, &enable))
     NOTREACHED();
 
   GetDisplayManager()->SetDefaultMultiDisplayModeForCurrentDisplays(
       enable ? display::DisplayManager::UNIFIED
              : display::DisplayManager::EXTENDED);
 }
 
 }  // namespace options
 }  // namespace chromeos