Have panels respond to changes in work area on Linux.

ui/base/x/active_window_watcher_x_observer.h

Index: ui/base/x/active_window_watcher_x_observer.h
diff --git a/ui/base/x/active_window_watcher_x_observer.h b/ui/base/x/active_window_watcher_x_observer.h
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+++ b/ui/base/x/active_window_watcher_x_observer.h
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+// Copyright (c) 2011 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_X_ACTIVE_WINDOW_WATCHER_X_OBSERVER_H_
+#define UI_BASE_X_ACTIVE_WINDOW_WATCHER_X_OBSERVER_H_
+#pragma once
+
+#include <gdk/gdk.h>
+
+#include "ui/base/ui_export.h"
+
+namespace ui {
+
+class UI_EXPORT ActiveWindowWatcherXObserver {
+ public:
+  // |active_window| will be NULL if the active window isn't one of Chrome's.
+  virtual void ActiveWindowChanged(GdkWindow* active_window) = 0;
+
+ protected:
+  virtual ~ActiveWindowWatcherXObserver() {}
+};
+
+}  // namespace ui
+
+#endif  // UI_BASE_X_ACTIVE_WINDOW_WATCHER_X_OBSERVER_H_