Support dragging panels to stack and snap.

chrome/browser/ui/panels/panel_collection.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_COLLECTION_H_
 #define CHROME_BROWSER_UI_PANELS_PANEL_COLLECTION_H_
 
 #include "chrome/browser/ui/panels/panel_constants.h"
 #include "ui/gfx/point.h"
 #include "ui/gfx/rect.h"
@@ skipping 11 matching lines @@
     STACKED,   // panels are stacked together
   };
 
   // Masks that control how the panel is added and positioned.
   enum PositioningMask {
     // The panel is added and placed at default position that is decided by the
     // collection.
     DEFAULT_POSITION = 0x0,
     // The panel is being added based on its current known position.
     KNOWN_POSITION = 0x1,
+    // The panel is added and placed at top position (currently only used by
+    // stacked collection)
+    TOP_POSITION = 0x2,
     // Do not update panel bounds. Only valid with DEFAULT_POSIITON.
-    DO_NOT_UPDATE_BOUNDS = 0x2,
+    DO_NOT_UPDATE_BOUNDS = 0x4,
     // Wait for a brief delay before refreshing layout of the collection after
     // adding panel to the collection. If not set, the collection will refresh
     // its layout immediately.
-    DELAY_LAYOUT_REFRESH = 0x4,
+    DELAY_LAYOUT_REFRESH = 0x8,
+    // Do not refresh layout. Used by stacking.
+    NO_LAYOUT_REFRESH = 0x10
   };
 
   Type type() const { return type_; }
 
   // Called when the display area is changed.
   virtual void OnDisplayAreaChanged(const gfx::Rect& old_display_area) = 0;
 
   // Updates the positioning of all panels in the collection, usually as
   // a result of removing or resizing a panel in collection.
   virtual void RefreshLayout() = 0;
@@ skipping 72 matching lines @@
   virtual void UpdatePanelOnCollectionChange(Panel* panel) = 0;
 
  protected:
   explicit PanelCollection(Type type);
   virtual ~PanelCollection();
 
   const Type type_;  // Type of this panel collection.
 };
 
 #endif  // CHROME_BROWSER_UI_PANELS_PANEL_COLLECTION_H_