Support auto-hide taskbar for panels on Windows.

chrome/browser/ui/panels/auto_hide_bottom_bar.h

+// 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 CHROME_BROWSER_UI_PANELS_AUTO_HIDE_BOTTOM_BAR_H_
+#define CHROME_BROWSER_UI_PANELS_AUTO_HIDE_BOTTOM_BAR_H_
+#pragma once
+
+#include "base/memory/ref_counted.h"
+
+namespace gfx {
+class Rect;
+}
+
+// Encapsulates the logic to deal with always-on-top system/app bar that is
+// located at the bottom of the screen and set to auto-hide, like Windows

[jennb, 2011/08/23 20:28:34]

Just thinking ahead:  this one handles bottom of screen only. Would we need a
separate class for task/app bars on the left/right of screen, or would we extend
this class to handle left/right cases as well? 

[jianli, 2011/08/26 00:18:16]

Refactored to handle all other edges.

+// taskbar or MacOSX dock.
+// Note that the ref count is needed by using PostTask in the implementation of
+// MockAutoHideBottomBar that derives from AutoHideBottomBar.
+class AutoHideBottomBar : public base::RefCountedThreadSafe<AutoHideBottomBar> {
+ public:
+  enum Visibility {
+    VISIBLE,
+    ANIMATING,
+    HIDDEN
+  };
+
+  // Observer can listen to various events regarding the bottom bar changes.
+  class Observer {
+   public:
+    virtual void OnAutoHideBottomBarVisibilityChanged(
+        Visibility visibility) = 0;
+    virtual void OnAutoHideBottomBarHeightChanged(int height) = 0;
+  };
+
+  static AutoHideBottomBar* Create(Observer* observer);
+
+  virtual ~AutoHideBottomBar() { }
+
+  // This should be called each time when the work area is changed. We only
+  // care about the bottom bar that sits on the screen that hosts the specified
+  // work area.
+  virtual void UpdateWorkArea(const gfx::Rect& work_area) = 0;
+
+  // Returns true if the auto-hide bottom bar is enabled.
+  virtual bool IsEnabled() = 0;

[jennb, 2011/08/23 20:28:34]

After reading more, I realize this value does double duty as both a boolean for
is-auto-hide-enabled and a boolean for is-system-bar-aligned-to-bottom.  I wish
there was some way to make this clearer than "IsEnabled", but I can live with it
if not.

[jianli, 2011/08/26 00:18:16]

Now it takes an alignment parameter.

+
+  // Returns the fixed height of the bottom bar. Note that the height remains
+  // unchanged no matter whether the bottom bar is brought up or down.
+

[jennb, 2011/08/23 20:28:34]

Extra blank line?

[jianli, 2011/08/26 00:18:16]

Not needed. Removed.

+  // Returns the height of bottom bar that corresponds to Visibility VISIBLE.
+  // This value does not depend on current bar's Visibility. The visible height
+  // of the bar when it's HIDDEN is usually between 0 and a few pixels.
+  virtual int GetHeight() = 0;
+
+  virtual Visibility GetVisibility() = 0;
+};
+
+#endif  // CHROME_BROWSER_UI_PANELS_AUTO_HIDE_BOTTOM_BAR_H_