Remove implementation of Panels on OSes other than ChromeOS.

chrome/browser/ui/panels/test_panel_active_state_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 CHROME_BROWSER_UI_PANELS_TEST_PANEL_ACTIVE_STATE_OBSERVER_H_
-#define CHROME_BROWSER_UI_PANELS_TEST_PANEL_ACTIVE_STATE_OBSERVER_H_
-
-#include "base/macros.h"
-#include "chrome/browser/ui/panels/test_panel_notification_observer.h"
-
-class Panel;
-
-// Custom notification observer for waiting on panel active state.
-// Modeled after ui_test_utils notification observers.
-class PanelActiveStateObserver : public TestPanelNotificationObserver {
- public:
-  // Register to listen for panel active state change notifications
-  // for the specified panel to detect a change to the expected active
-  // state.
-  PanelActiveStateObserver(Panel* panel, bool expect_active);
-  ~PanelActiveStateObserver() override;
-
- private:
-  // TestNotificationObserver override:
-  bool AtExpectedState() override;
-
-  Panel* panel_;
-  bool expect_active_;
-
-  DISALLOW_COPY_AND_ASSIGN(PanelActiveStateObserver);
-};
-
-#endif  // CHROME_BROWSER_UI_PANELS_TEST_PANEL_ACTIVE_STATE_OBSERVER_H_