Remove implementation of Panels on OSes other than ChromeOS.

chrome/browser/ui/panels/test_panel_collection_squeeze_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_COLLECTION_SQUEEZE_OBSERVER_H_
-#define CHROME_BROWSER_UI_PANELS_TEST_PANEL_COLLECTION_SQUEEZE_OBSERVER_H_
-
-#include "base/macros.h"
-#include "chrome/browser/ui/panels/test_panel_notification_observer.h"
-
-class DockedPanelCollection;
-class Panel;
-
-// Custom notification observer for waiting on panel collection that squeezes
-// its panels to reflect a certain state.
-// Modeled after ui_test_utils notification observers.
-class PanelCollectionSqueezeObserver : public TestPanelNotificationObserver {
- public:
-  // Register to listen for panel collection updated notifications
-  // from the specified collection to detect a change to the state
-  // where the |active_panel| is at full width and all other
-  // panels in the collection are squeezed.
-  PanelCollectionSqueezeObserver(DockedPanelCollection* collection,
-                                 Panel* active_panel);
-  ~PanelCollectionSqueezeObserver() override;
-
- private:
-  // TestNotificationObserver override:
-  bool AtExpectedState() override;
-
-  bool IsSqueezed(Panel* panel);
-
-  DockedPanelCollection* panel_collection_;
-  Panel* active_panel_;
-
-  DISALLOW_COPY_AND_ASSIGN(PanelCollectionSqueezeObserver);
-};
-
-#endif  // CHROME_BROWSER_UI_PANELS_TEST_PANEL_COLLECTION_SQUEEZE_OBSERVER_H_