Refactor intra-strip panel drags by introducing PanelDragController.

chrome/browser/ui/panels/panel_strip.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_PANEL_STRIP_H_
 #define CHROME_BROWSER_UI_PANELS_PANEL_STRIP_H_
 #pragma once
 
 #include "ui/gfx/rect.h"
 
@@ skipping 44 matching lines @@
   // draw attention state.
   virtual void OnPanelAttentionStateChanged(Panel* panel) = 0;
 
   // Updates the display to show |panel| as active.
   virtual void ActivatePanel(Panel* panel) = 0;
 
   // Updates the display to show |panel| as  minimized/restored.
   virtual void MinimizePanel(Panel* panel) = 0;
   virtual void RestorePanel(Panel* panel) = 0;
 
+  // Returns true if |panel| is draggable.
+  virtual bool CanDragPanel(Panel* panel) const = 0;
+
+  // Drags |panel| in the bounds of this strip.
+  virtual void StartDraggingPanel(Panel* panel) = 0;
+  // |delta_x| and |delta_y| are the offset from the last mouse position when
+  // DragPanel or StartDraggingPanel is called.

[jennb, 2012/02/16 22:31:00]

Not sure I understand the comment because there's no mouse position passed to
StartDraggingPanel() nor DragPanel().

[jianli, 2012/02/16 23:05:52]

We only care about how much the mouse has been moved since last time DragPanel
or StartDraggingPanel is called. The underlying code might choose to apply or
not apply these delta values to the origin of the panel being dragged. I've
updated the comment to make it clearer.

+  virtual void DragPanel(int delta_x, int delta_y) = 0;
+  virtual void EndDraggingPanel(bool cancelled) = 0;
+
  protected:
   explicit PanelStrip(Type type);
   virtual ~PanelStrip();
 
   const Type type_;  // Type of this panel strip.
 };
 
 #endif  // CHROME_BROWSER_UI_PANELS_PANEL_STRIP_H_