Add GrabWindowSnapshotAsync tests

ui/snapshot/snapshot_ios.mm

Index: ui/snapshot/snapshot_ios.mm
diff --git a/ui/snapshot/snapshot_ios.mm b/ui/snapshot/snapshot_ios.mm
index b121d4249726c0e1d41d3a95148355616ecd4750..425192f56b04819c7a921e64ac818313fa889548 100644
--- a/ui/snapshot/snapshot_ios.mm
+++ b/ui/snapshot/snapshot_ios.mm
@@ -23,7 +23,7 @@ bool GrabWindowSnapshot(gfx::NativeWindow window,
   return false;
 }
 
-SNAPSHOT_EXPORT void GrabWindowSnapshotAsync(
+void GrabWindowSnapshotAndScaleAsync(
     gfx::NativeWindow window,
     const gfx::Rect& snapshot_bounds,
     const gfx::Size& target_size,
@@ -32,4 +32,12 @@ 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