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

ui/gfx/screen_mac.mm

Index: ui/gfx/screen_mac.mm
diff --git a/ui/gfx/screen_mac.mm b/ui/gfx/screen_mac.mm
index b33af2da12999480b719b605020583ba306958bc..54e7aadc17e0ab8163ce06bb0066e6d7e2907f8d 100644
--- a/ui/gfx/screen_mac.mm
+++ b/ui/gfx/screen_mac.mm
@@ -95,9 +95,9 @@ class ScreenMac : public gfx::Screen {
     return gfx::ScreenPointFromNSPoint([NSEvent mouseLocation]);
   }
 
-  gfx::NativeWindow GetWindowUnderCursor() override {
+  bool IsWindowUnderCursor(gfx::NativeWindow window) override {
     NOTIMPLEMENTED();
-    return gfx::NativeWindow();
+    return false;
   }
 
   gfx::NativeWindow GetWindowAtScreenPoint(const gfx::Point& point) override {