Implement large cursors in Mushrome.

ash/shell_port.h

Index: ash/shell_port.h
diff --git a/ash/shell_port.h b/ash/shell_port.h
index a2844bead1531223a0a3486c5ed8d8bfe8a3fc77..a46326154a5eece5b9db305f8f68dfc0fe913382 100644
--- a/ash/shell_port.h
+++ b/ash/shell_port.h
@@ -33,6 +33,10 @@ namespace gfx {
 class Point;
 }
 
+namespace ui {
+enum class CursorSize;
+}
+
 namespace views {
 class PointerWatcher;
 enum class PointerWatcherEventTypes;
@@ -102,6 +106,7 @@ class ASH_EXPORT ShellPort {
   virtual void UnlockCursor() = 0;
   virtual void ShowCursor() = 0;
   virtual void HideCursor() = 0;
+  virtual void SetCursorSize(ui::CursorSize cursor_size) = 0;
   virtual void SetGlobalOverrideCursor(
       base::Optional<ui::CursorData> cursor) = 0;
   virtual bool IsMouseEventsEnabled() = 0;