Make aura::clients take Window instead of RootWindow

ui/views/widget/desktop_aura/desktop_drop_target_win.h

Index: ui/views/widget/desktop_aura/desktop_drop_target_win.h
diff --git a/ui/views/widget/desktop_aura/desktop_drop_target_win.h b/ui/views/widget/desktop_aura/desktop_drop_target_win.h
index 3fde71f0a3ce834df5b1de24b6b8b59dc0cba86c..113fd75ce236e76958ecf74835e85e0b2b668b54 100644
--- a/ui/views/widget/desktop_aura/desktop_drop_target_win.h
+++ b/ui/views/widget/desktop_aura/desktop_drop_target_win.h
@@ -10,7 +10,6 @@
 #include "ui/base/dragdrop/drop_target_win.h"
 
 namespace aura {
-class RootWindow;
 namespace client {
 class DragDropDelegate;
 }
@@ -29,7 +28,7 @@ namespace views {
 class DesktopDropTargetWin : public ui::DropTargetWin,
                              public aura::WindowObserver {
  public:
-  DesktopDropTargetWin(aura::RootWindow* root_window, HWND window);
+  DesktopDropTargetWin(aura::Window* root_window, HWND window);
   virtual ~DesktopDropTargetWin();
 
  private:
@@ -64,7 +63,7 @@ class DesktopDropTargetWin : public ui::DropTargetWin,
   void NotifyDragLeave();
 
   // The root window associated with this drop target.
-  aura::RootWindow* root_window_;
+  aura::Window* root_window_;
 
   // The Aura window that is currently under the cursor. We need to manually
   // keep track of this because Windows will only call our drag enter method