Add GrabWindowSnapshotAsync tests

ui/snapshot/snapshot.h

Index: ui/snapshot/snapshot.h
diff --git a/ui/snapshot/snapshot.h b/ui/snapshot/snapshot.h
index d6fb6b8b0183326b7b2414e050d1f17bac2dc918..7ccd8b4ac58e54859cb323dffd1f4744bc3c4a25 100644
--- a/ui/snapshot/snapshot.h
+++ b/ui/snapshot/snapshot.h
@@ -28,7 +28,7 @@ namespace ui {
 // intended to be used for debugging purposes where no BrowserProcess instance
 // is available (ie. tests). This function is synchronous, so it should NOT be
 // used in a result of user action. Use asynchronous GrabWindowSnapshotAsync()
-// instead.
+// instead on supported platforms.
 SNAPSHOT_EXPORT bool GrabWindowSnapshot(
     gfx::NativeWindow window,
     std::vector<unsigned char>* png_representation,
@@ -39,16 +39,21 @@ SNAPSHOT_EXPORT bool GrabViewSnapshot(
     std::vector<unsigned char>* png_representation,
     const gfx::Rect& snapshot_bounds);
 
-// GrabWindowSnapshotAsync() copies snapshot of |source_rect| from window and
-// scales it to |target_size| asynchronously.
 typedef base::Callback<void(const gfx::Image& snapshot)>
     GrabWindowSnapshotAsyncCallback;
-SNAPSHOT_EXPORT void GrabWindowSnapshotAsync(
+// GrabWindowSnapshotAndScaleAsync() copies snapshot of |source_rect| from
+// window and scales it to |target_size| asynchronously.
+SNAPSHOT_EXPORT void GrabWindowSnapshotAndScaleAsync(
     gfx::NativeWindow window,
     const gfx::Rect& source_rect,
     const gfx::Size& target_size,
     scoped_refptr<base::TaskRunner> background_task_runner,
     const GrabWindowSnapshotAsyncCallback& callback);
+SNAPSHOT_EXPORT void GrabWindowSnapshotAsync(
+    gfx::NativeWindow window,
+    const gfx::Rect& source_rect,
+    scoped_refptr<base::TaskRunner> background_task_runner,
+    const GrabWindowSnapshotAsyncCallback& callback);
 
 }  // namespace ui