chromeos: Add external brightness control to chrome://flags.

ash/system/chromeos/brightness/tray_brightness.cc

 // Copyright 2013 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 "ash/system/chromeos/brightness/tray_brightness.h"
 
 #include "ash/accelerators/accelerator_controller.h"
 #include "ash/ash_constants.h"
+#include "ash/display/display_manager.h"
 #include "ash/metrics/user_metrics_recorder.h"
 #include "ash/shell.h"
 #include "ash/system/brightness_control_delegate.h"
 #include "ash/system/tray/fixed_sized_image_view.h"
 #include "ash/system/tray/system_tray_delegate.h"
 #include "ash/system/tray/system_tray_notifier.h"
 #include "ash/system/tray/tray_constants.h"
 #include "base/bind.h"
 #include "base/message_loop/message_loop.h"
 #include "base/strings/utf_string_conversions.h"
@@ skipping 193 matching lines @@
   HandleBrightnessChanged(percent, user_initiated);
 }
 
 void TrayBrightness::HandleBrightnessChanged(double percent,
                                              bool user_initiated) {
   current_percent_ = percent;
   got_current_percent_ = true;
 
   if (brightness_view_)
     brightness_view_->SetBrightnessPercent(percent);
+
   if (!user_initiated)
     return;
 
+  // Never show the bubble on systems that lack internal displays: if an
+  // external display's brightness is changed, it may already display the new
+  // level via an on-screen display.
+  if (!Shell::GetInstance()->display_manager()->HasInternalDisplay())
+    return;
+
   if (brightness_view_)
     SetDetailedViewCloseDelay(kTrayPopupAutoCloseDelayInSeconds);
   else
     PopupDetailedView(kTrayPopupAutoCloseDelayInSeconds, false);
 }
 
 }  // namespace internal
 }  // namespace ash