Add ScreenPositionClient::ConvertNativePointToScreen.

ui/aura/client/screen_position_client.h

Index: ui/aura/client/screen_position_client.h
diff --git a/ui/aura/client/screen_position_client.h b/ui/aura/client/screen_position_client.h
index 17e73d88b459f3dfe9ffa5bf7ee2b3884f438074..ac45d44b656f3fbb7c33e514282c25e27d9baa96 100644
--- a/ui/aura/client/screen_position_client.h
+++ b/ui/aura/client/screen_position_client.h
@@ -31,6 +31,13 @@ class AURA_EXPORT ScreenPositionClient {
                                     gfx::Point* point) = 0;
   virtual void ConvertPointFromScreen(const Window* window,
                                       gfx::Point* point) = 0;
+  // Converts the |screen_point| from a given |window|'s native screen
+  // coordinate space into screen coordinate space.
+  // A typical example of using this function instead of ConvertPointToScreen is
+  // when X's native input is captured by a drag operation.
+  // See the comments in ash::wm::GetRootWindowRelativeToWindow for details.

[oshima, 2012/09/18 10:02:34]

This description isn't exactly correct, i think. 
This is to convert an event whose location is outside of
the mouse event target's root (mouse_moved_handler_ i believe). Passive grab is
one scenario and aura capture is another scenario. (see my comment in
coordinate_conversion.cc)

[mazda, 2012/09/18 16:35:01]

I'm thinking about letting this function handle only passive grab case because
trying to handle another scenario causes problems when bounds in native and
scree overlaps as we talked before.

+  virtual void ConvertNativePointToScreen(Window* window,
+                                          gfx::Point* point) = 0;
   // Sets the bounds of the window. The implementation is responsible
   // for finding out and translating the right coordinates for the |window|.
   virtual void SetBounds(Window* window,