Refactor intra-strip panel drags by introducing PanelDragController.

chrome/browser/ui/panels/docked_panel_strip.h

Index: chrome/browser/ui/panels/docked_panel_strip.h
diff --git a/chrome/browser/ui/panels/docked_panel_strip.h b/chrome/browser/ui/panels/docked_panel_strip.h
index 55d6f54798b3e055765cb1ac789797434be16ee1..9e67688097e10ca6dc519c24aa2721cf0587780c 100644
--- a/chrome/browser/ui/panels/docked_panel_strip.h
+++ b/chrome/browser/ui/panels/docked_panel_strip.h
@@ -53,11 +53,10 @@ class DockedPanelStrip : public PanelStrip,
   virtual void ActivatePanel(Panel* panel) OVERRIDE;
   virtual void MinimizePanel(Panel* panel) OVERRIDE;
   virtual void RestorePanel(Panel* panel) OVERRIDE;
-
-  // Drags the given panel.
-  void StartDragging(Panel* panel);
-  void Drag(int delta_x);
-  void EndDragging(bool cancelled);
+  virtual bool CanDragPanel(Panel* panel) const OVERRIDE;
+  virtual void StartDraggingPanel(Panel* panel) OVERRIDE;
+  virtual void DragPanel(int delta_x, int delta_y) OVERRIDE;
+  virtual void EndDraggingPanel(bool cancelled) OVERRIDE;
 
   // Invoked when a panel's expansion state changes.
   void OnPanelExpansionStateChanged(Panel* panel);