Extract the code for supporing extended desktop from WorkspaceWindowResizer into DragWindowResizer.

ash/wm/window_resizer.h

Index: ash/wm/window_resizer.h
diff --git a/ash/wm/window_resizer.h b/ash/wm/window_resizer.h
index d8c398fbdb63be01b72495748f075fe7facdd2cd..bc46df85e31a51b9adb9d2932678303db03eee87 100644
--- a/ash/wm/window_resizer.h
+++ b/ash/wm/window_resizer.h
@@ -124,7 +124,7 @@ class ASH_EXPORT WindowResizer {
 
 // Creates a WindowResizer for |window|. This can return a scoped_ptr
 // initialized with NULL if |window| should not be resized nor dragged.
-scoped_ptr<WindowResizer> CreateWindowResizer(
+ASH_EXPORT scoped_ptr<WindowResizer> CreateWindowResizer(
     aura::Window* window,
     const gfx::Point& point_in_parent,
     int window_component);