Add GrabWindowSnapshotAsync tests

ui/snapshot/snapshot_mac.mm

Index: ui/snapshot/snapshot_mac.mm
diff --git a/ui/snapshot/snapshot_mac.mm b/ui/snapshot/snapshot_mac.mm
index 9057e6635b7982af7e569f890d385da652edbb45..2ebdf543c84811ae9949602dd8b97bc89c53f9c6 100644
--- a/ui/snapshot/snapshot_mac.mm
+++ b/ui/snapshot/snapshot_mac.mm
@@ -73,7 +73,7 @@ bool GrabWindowSnapshot(gfx::NativeWindow window,
       snapshot_bounds);
 }
 
-SNAPSHOT_EXPORT void GrabWindowSnapshotAsync(
+void GrabWindowSnapshotAndScaleAsync(
     gfx::NativeWindow window,
     const gfx::Rect& snapshot_bounds,
     const gfx::Size& target_size,
@@ -82,4 +82,12 @@ SNAPSHOT_EXPORT void GrabWindowSnapshotAsync(
   NOTIMPLEMENTED();
 }
 
+void GrabWindowSnapshotAsync(
+    gfx::NativeWindow window,
+    const gfx::Rect& source_rect,
+    scoped_refptr<base::TaskRunner> background_task_runner,
+    const GrabWindowSnapshotAsyncCallback& callback) {
+  NOTIMPLEMENTED();
+}
+
 }  // namespace ui