gfx::Screen: Replace GetWindowUnderCursor() with IsWindowUnderCursor().

ui/gfx/screen_ios.mm

Index: ui/gfx/screen_ios.mm
diff --git a/ui/gfx/screen_ios.mm b/ui/gfx/screen_ios.mm
index 6ace9c8ed2975a68a9be4b7216539cf2ebd03581..ec00c1b6401d356231c09eb2ea1fd2d0d7be4bea 100644
--- a/ui/gfx/screen_ios.mm
+++ b/ui/gfx/screen_ios.mm
@@ -17,9 +17,9 @@ class ScreenIos : public gfx::Screen {
     return gfx::Point(0, 0);
   }
 
-  gfx::NativeWindow GetWindowUnderCursor() override {
+  bool IsWindowUnderCursor(gfx::NativeWindow window) override {
     NOTIMPLEMENTED();
-    return gfx::NativeWindow();
+    return false;
   }
 
   gfx::NativeWindow GetWindowAtScreenPoint(const gfx::Point& point) override {