Support dragging panels to stack and snap.

chrome/browser/ui/panels/stacked_panel_collection.h

Index: chrome/browser/ui/panels/stacked_panel_collection.h
diff --git a/chrome/browser/ui/panels/stacked_panel_collection.h b/chrome/browser/ui/panels/stacked_panel_collection.h
index 8d746ba5ed29c02945e0c452cd14caa62b843a1f..9d01d4f55d657b744d777e585f423d0487859c59 100644
--- a/chrome/browser/ui/panels/stacked_panel_collection.h
+++ b/chrome/browser/ui/panels/stacked_panel_collection.h
@@ -9,9 +9,15 @@
 #include <vector>
 #include "base/basictypes.h"
 #include "chrome/browser/ui/panels/panel_collection.h"
+#include "chrome/browser/ui/panels/panel_constants.h"
+#include "ui/gfx/native_widget_types.h"
 #include "ui/gfx/rect.h"
 
+class NativePanelStack;
 class PanelManager;
+namespace gfx {
+class Vector2d;
+}
 
 class StackedPanelCollection : public PanelCollection {
  public:
@@ -53,17 +59,37 @@ class StackedPanelCollection : public PanelCollection {
   Panel* GetPanelAbove(Panel* panel) const;
   bool HasPanel(Panel* panel) const;
 
-  bool empty() const { return panels_.empty(); }
+  gfx::NativeWindow GetNativeWindow() const;
+
+  void MoveAllDraggingPanels(const gfx::Vector2d& delta_origin);
+
   int num_panels() const { return panels_.size(); }
   const Panels& panels() const { return panels_; }
-  Panel* top_panel() const { return panels_.front(); }
-  Panel* bottom_panel() const { return panels_.back(); }
+  Panel* top_panel() const { return panels_.empty() ? NULL : panels_.front(); }
+  Panel* bottom_panel() const {
+    return panels_.empty() ? NULL : panels_.back();
+  }
 
  private:
-  PanelManager* panel_manager_;  // Weak, owns us.
+  struct PanelPlacement {
+    Panel* panel;
+    gfx::Point position;
+    // Used to remember the top panel, if different from |panel|, for use when

[Dmitry Titov, 2013/01/09 02:29:50]

Could you improve this comment, it's not clear waht "for use when restore it"
means, w/o context.

[jianli, 2013/01/09 21:00:59]

Done.

+    // restoring it.
+    Panel* top_panel;
+
+    PanelPlacement() : panel(NULL) { }

[Dmitry Titov, 2013/01/09 02:29:50]

initialize top_panel(NULL) too

[jianli, 2013/01/09 21:00:59]

Done.

+  };
+
+  PanelManager* panel_manager_;
+
+  NativePanelStack* native_stack_;  // Weak, own us.
 
   Panels panels_;  // The top panel is in the front of the list.
 
+  // Used to save the placement information for a panel.
+  PanelPlacement saved_panel_placement_;
+
   DISALLOW_COPY_AND_ASSIGN(StackedPanelCollection);
 };