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(const Panel* panel) const = 0;
+
+  // Drags |panel| in the bounds of this strip.
+  virtual void StartDraggingPanel(Panel* panel) = 0;
+  // |delta_x| and |delta_y| denotes how much the mouse has been moved since
+  // last time when DragPanel or StartDraggingPanel is called.
+  virtual void DragPanel(Panel* panel, int delta_x, int delta_y) = 0;
+  virtual void EndDraggingPanel(Panel* panel, 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_