Allow the user to drag a window from one display to another

ash/wm/workspace/workspace_window_resizer.h

Index: ash/wm/workspace/workspace_window_resizer.h
diff --git a/ash/wm/workspace/workspace_window_resizer.h b/ash/wm/workspace/workspace_window_resizer.h
index 79df0ba5b60b87c36838a0b20ebf03211c853f32..f49f7cb1bdad9f631c3e858a0b91b76afef7b924 100644
--- a/ash/wm/workspace/workspace_window_resizer.h
+++ b/ash/wm/workspace/workspace_window_resizer.h
@@ -11,6 +11,10 @@
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 
+namespace aura {
+class RootWindow;
+}  // namespace aura
+
 namespace ash {
 namespace internal {
 
@@ -106,12 +110,16 @@ class ASH_EXPORT WorkspaceWindowResizer : public WindowResizer {
   int PrimaryAxisSize(const gfx::Size& size) const;
   int PrimaryAxisCoordinate(int x, int y) const;
 
-  // Updates the bounds of the phantom window.
+  // Updates the bounds of the phantom window for window snapping.
   void UpdatePhantomWindow(
       const gfx::Point& location,
       const gfx::Rect& bounds,
       int grid_size);
 
+  // Updates the bounds of the phantom window for window dragging.
+  void UpdateDragPhantomWindow(aura::RootWindow* another_root,
+                               const gfx::Rect& window_bounds_in_screen);
+
   // Restacks the windows z-order position so that one of the windows is at the
   // top of the z-order, and the rest directly underneath it.
   void RestackWindows();
@@ -157,6 +165,11 @@ class ASH_EXPORT WorkspaceWindowResizer : public WindowResizer {
   // is a grid and the caption is being dragged.
   scoped_ptr<PhantomWindowController> phantom_window_controller_;
 
+  // For now, we show a phantom window on the other root window during dragging.
+  // TODO(yusukes): Show a semi-transparent image (screen shot) of the window
+  // instead.
+  scoped_ptr<PhantomWindowController> drag_phantom_window_controller_;
+
   // Used to determine the target position of a snap.
   scoped_ptr<SnapSizer> snap_sizer_;