aura-x11: Add custom web cursor support.

ui/aura/root_window.h

Index: ui/aura/root_window.h
diff --git a/ui/aura/root_window.h b/ui/aura/root_window.h
index c84d6977dfc48b3897799e1cf222749690cae16e..2e9189c01bb692f3f460e31091f8c5593624d23d 100644
--- a/ui/aura/root_window.h
+++ b/ui/aura/root_window.h
@@ -83,9 +83,13 @@ class AURA_EXPORT RootWindow : public ui::CompositorDelegate,
   // Sets the currently-displayed cursor. If the cursor was previously hidden
   // via ShowCursor(false), it will remain hidden until ShowCursor(true) is
   // called, at which point the cursor that was last set via SetCursor() will be
-  // used.
+  // used. To set a custom cursor, use SetCustomCursor instead.
   void SetCursor(gfx::NativeCursor cursor);
 
+  // Sets a custom cursor for the display. This interacts with ShowCursor the
+  // same as SetCursor (see above).
+  void SetCustomCursor(const gfx::PlatformCursor& cursor);
+
   // Shows or hides the cursor.
   void ShowCursor(bool show);