Support dragging panels to stack and snap.

chrome/browser/ui/panels/native_panel_stack.h

Index: chrome/browser/ui/panels/native_panel_stack.h
diff --git a/chrome/browser/ui/panels/native_panel_stack.h b/chrome/browser/ui/panels/native_panel_stack.h
new file mode 100644
index 0000000000000000000000000000000000000000..9cb0c30ec1a4b85f30ba5ae36058d527782a1f42
--- /dev/null
+++ b/chrome/browser/ui/panels/native_panel_stack.h
@@ -0,0 +1,35 @@
+// 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_NATIVE_PANEL_STACK_H_
+#define CHROME_BROWSER_UI_PANELS_NATIVE_PANEL_STACK_H_
+
+#include "ui/gfx/native_widget_types.h"
+
+class StackedPanelCollection;
+namespace gfx {
+class Rect;
+}
+
+// An interface that encapsulates the platform-specific behaviors that are
+// needed to support multiple panels that are stacked together. A native
+// window might be created to enclose all the panels in the stack. The lifetime
+// of the class that implements this interface is managed by itself.
+class NativePanelStack {
+  friend class StackedPanelCollection;
+
+ public:
+  // The StackedPanelCollection instance is passed and owned by the
+  // NativePanelStack instance that is being created.
+  static NativePanelStack* Create(StackedPanelCollection* stack);
+  virtual ~NativePanelStack() {}
+
+ protected:
+  virtual void Close() = 0;

[Dmitry Titov, 2013/01/10 00:16:24]

Could you add a comment about who and when calls this Close(). This would be
useful to understanding the lifetime of the object.

[jianli, 2013/01/10 02:05:37]

Done.

+  virtual void OnPanelAddedOrRemoved() = 0;

[Dmitry Titov, 2013/01/10 00:16:24]

This feels like it should get a Panel* argument, then we can remove
UpdatePanelStackingProperty from NativePanel

[jianli, 2013/01/10 02:05:37]

Done.

+  virtual gfx::NativeWindow GetNativeWindow() const = 0;
+  virtual void SetBounds(const gfx::Rect& bounds) = 0;

[Dmitry Titov, 2013/01/10 00:16:24]

SetBounds - also a comment would be useful about who calls that.

[jianli, 2013/01/10 02:05:37]

Done.

+};
+
+#endif  // CHROME_BROWSER_UI_PANELS_NATIVE_PANEL_STACK_H_