Support dragging panels to stack and snap.

chrome/browser/ui/panels/native_panel_stack.h

+// Copyright (c) 2013 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 "base/memory/scoped_ptr.h"
+
+class Panel;
+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 {
+ public:
+  // Creates and returns a NativePanelStack instance whose lifetime is managed
+  // by itself and it will be valid until Close is called. NativePanelStack
+  // also owns the StackedPanelCollection instance being passed here.
+  static NativePanelStack* Create(scoped_ptr<StackedPanelCollection> stack);
+
+  virtual ~NativePanelStack() {}
+
+ protected:
+  friend class StackedPanelCollection;
+
+  // Called when the stack is to be closed. This will destruct the
+  // NativePanelStack instance which causes the StackedPanelCollection
+  // instance to be also destructed since the former owns the later.
+  virtual void Close() = 0;
+
+  // Called when |panel| is being added to or removed from the stack.
+  virtual void OnPanelAddedOrRemoved(Panel* panel) = 0;
+
+  // Sets the bounds that is big enough to enclose all panels in the stack.
+  virtual void SetBounds(const gfx::Rect& bounds) = 0;
+};
+
+#endif  // CHROME_BROWSER_UI_PANELS_NATIVE_PANEL_STACK_H_