Support dragging panels to stack and snap.

chrome/browser/ui/panels/native_panel_stack.h

+// 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_
+
+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 {
+  friend class StackedPanelCollection;

[dcheng, 2013/01/10 22:39:03]

Isn't typical convention to put these in an explicit private: section?

[jianli, 2013/01/10 23:23:23]

Done.

+
+ public:
+  // The StackedPanelCollection instance is passed and owned by the
+  // NativePanelStack instance that is being created.
+  static NativePanelStack* Create(StackedPanelCollection* stack);

[dcheng, 2013/01/10 22:39:03]

I know we don't do it elsewhere at the moment, but we may want to consider using
scoped_ptr where applicable here. In particular, we could probably change this
to be:
static scoped_ptr<NativePanelStack> Create(scoped_ptr<StackedPanelCollection>
stack); to indicate the ownership transfers, rather than depending on comments.

[jianli, 2013/01/10 23:23:23]

No, we can't do that since the lifetime of NativePanelStack is managed by itself
and it will be destructed after Close() is called. I updated the comment to make
it more clear.

[dcheng, 2013/01/10 23:43:01]

At the very least, StackedPanelCollection should still be passed by scoped_ptr
since a NativePanelStack should and will take ownership of it.

+  virtual ~NativePanelStack() {}
+
+ protected:
+  // 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_