Have panels respond to changes in work area on Linux.

ui/base/x/work_area_watcher_x.h

Index: ui/base/x/work_area_watcher_x.h
diff --git a/ui/base/x/work_area_watcher_x.h b/ui/base/x/work_area_watcher_x.h
new file mode 100644
index 0000000000000000000000000000000000000000..592465f7f457eaad48b187060b7a9bbce8cdec32
--- /dev/null
+++ b/ui/base/x/work_area_watcher_x.h
@@ -0,0 +1,51 @@
+// 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_WORK_AREA_WATCHER_X_H_
+#define UI_BASE_X_WORK_AREA_WATCHER_X_H_
+#pragma once
+
+#include "base/memory/singleton.h"
+#include "base/observer_list.h"
+#include "ui/base/ui_export.h"
+#include "ui/base/x/x11_util.h"
+
+namespace ui {
+
+// This is a helper class that is used to keep track of changes to work area.
+// Add an observer to track changes.
+class UI_EXPORT WorkAreaWatcherX {
+ public:
+  class Observer {

[sky, 2011/11/18 17:54:22]

Move this into it's own header.

[prasadt, 2011/11/18 22:31:42]

I see nested classes being in the same header as a common pattern in code. Any
reason why it is different in this case?

[sky, 2011/11/18 22:44:58]

From the style guide: 'Prefer putting delegate classes in their own header
files. Implementors of the delegate interface will often be included elsewhere,
which will often cause more coupling with the header of the main class.' We need
to update more classes to follow this pattern.

[prasadt, 2011/11/21 23:36:49]

Done.

+   public:
+    virtual void WorkAreaChanged() = 0;
+
+   protected:
+    virtual ~Observer() {}
+  };
+
+  static WorkAreaWatcherX* GetInstance();
+  static void AddObserver(Observer* observer);
+  static void RemoveObserver(Observer* observer);
+  static Atom GetPropertyAtom();
+
+  // Sends a notification out through the NotificationService that the work
+  // area has changed.
+  static void Notify();
+
+ private:
+  friend struct DefaultSingletonTraits<WorkAreaWatcherX>;
+
+  WorkAreaWatcherX() { }

[sky, 2011/11/18 17:54:22]

Don't inline these.

[prasadt, 2011/11/18 22:31:42]

Done.

+  ~WorkAreaWatcherX() { }
+  void NotifyWorkAreaChanged();
+
+  ObserverList<Observer> observers_;
+
+  DISALLOW_COPY_AND_ASSIGN(WorkAreaWatcherX);
+};
+
+}  // namespace ui
+
+#endif  // UI_BASE_X_WORK_AREA_WATCHER_X_H_