Support detaching/attaching panels via inter-strip drags.

chrome/browser/ui/panels/panel_strip.h

Index: chrome/browser/ui/panels/panel_strip.h
diff --git a/chrome/browser/ui/panels/panel_strip.h b/chrome/browser/ui/panels/panel_strip.h
index c1da8f4c5bf6d5cdd518b88acbb5796ebb237a71..422bb4a12fbad0f8203811ca9f4455850c4251fb 100644
--- a/chrome/browser/ui/panels/panel_strip.h
+++ b/chrome/browser/ui/panels/panel_strip.h
@@ -6,6 +6,7 @@
 #define CHROME_BROWSER_UI_PANELS_PANEL_STRIP_H_
 #pragma once
 
+#include "ui/gfx/point.h"
 #include "ui/gfx/rect.h"
 
 class Panel;
@@ -66,15 +67,36 @@ class PanelStrip {
   // Returns true if |panel| can be shown as active.
   virtual bool CanShowPanelAsActive(const Panel* panel) const = 0;
 
+  // Saves/restores/discards the placement information of |panel|. This is
+  // useful in bringing back the dragging panel to its original positioning
+  // when the drag is cancelled. After the placement information is saved,
+  // the caller should only call one of RestorePanelToSavedPlacement and
+  // DiscardSavedPanelPlacement.
+  virtual void SavePanelPlacement(Panel* panel) = 0;
+  virtual void RestorePanelToSavedPlacement() = 0;
+  virtual void DiscardSavedPanelPlacement() = 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;
+  // Starts dragging |panel| within this strip. The panel should already be
+  // in this strip.
+  virtual void StartDraggingPanelWithinStrip(Panel* panel) = 0;
+
+  // Drags |panel| within this strip.
+  // |delta_x| and |delta_y| represents the offset from the last mouse location
+  // when StartDraggingPanelWithinStrip or DragPanelWithinStrip is called.
+  virtual void DragPanelWithinStrip(Panel* panel, int delta_x, int delta_y) = 0;
+
+  // Ends dragging |panel| within this strip. |aborted| means the drag within
+  // this strip is aborted due to one of the following:
+  // 1) the drag leaves this strip and enters other strip
+  // 2) the drag gets cancelled
+  // If |aborted| is true, |panel| will stay as it is; otherwise, it will be
+  // moved to its finalized position.
+  // The drag controller is responsible for restoring the panel back to its
+  // original strip and position when the drag gets cancelled.
+  virtual void EndDraggingPanelWithinStrip(Panel* panel, bool aborted) = 0;
 
  protected:
   explicit PanelStrip(Type type);