Remove unused WorkAreaWatcherObserver

Bug: 122863
Change-Id: I9135498788382c89846d2be11f38fec3558f134d
Reviewed-on: https://chromium-review.googlesource.com/c/1258782Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Yoshiki Iguchi <yoshiki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601470}

ui/base/BUILD.gn

@@ -308,7 +308,6 @@ jumbo_component("base") {
     "win/window_event_target.h",
     "window_open_disposition.cc",
     "window_open_disposition.h",
-    "work_area_watcher_observer.h",
   ]
 
   if (is_posix) {

ui/base/work_area_watcher_observer.h

-// 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.
-
-#ifndef UI_BASE_WORK_AREA_WATCHER_OBSERVER_H_
-#define UI_BASE_WORK_AREA_WATCHER_OBSERVER_H_
-
-#include "ui/base/ui_base_export.h"
-
-namespace ui {
-
-// This interface should be implemented by classes that want to be notified
-// when the work area has changed due to something like screen resolution or
-// taskbar changes.
-class UI_BASE_EXPORT WorkAreaWatcherObserver {
- public:
-  virtual void WorkAreaChanged() = 0;
-
- protected:
-  virtual ~WorkAreaWatcherObserver() {}
-};
-
-}  // namespace ui
-
-#endif  // UI_BASE_WORK_AREA_WATCHER_OBSERVER_H_

ui/display/display_observer.h

@@ -14,8 +14,6 @@ namespace display {
 class Display;
 
 // Observers for display configuration changes.
-// TODO(oshima): consolidate |WorkAreaWatcherObserver| and
-// |DisplaySettingsProvier|. crbug.com/122863.
 class DISPLAY_EXPORT DisplayObserver : public base::CheckedObserver {
  public:
   enum DisplayMetric {