Use a base::OnceCallback instead of WebCompositeAndReadbackAsyncCallback.

This is now allowed across the Blink API, and also removes the need to write
manual "delete this;" code.

Change-Id: If5224aac68d6c96b7c6f7014580955e4922ea0bd
Reviewed-on: https://chromium-review.googlesource.com/1013062
Commit-Queue: Jeremy Roman <[email protected]>
Reviewed-by: Kentaro Hara <[email protected]>
Reviewed-by: Antoine Labour <[email protected]>
Cr-Commit-Position: refs/heads/master@{#551275}
diff --git a/content/renderer/gpu/render_widget_compositor.h b/content/renderer/gpu/render_widget_compositor.h
index 9be9627..af6391f 100644
--- a/content/renderer/gpu/render_widget_compositor.h
+++ b/content/renderer/gpu/render_widget_compositor.h
@@ -150,7 +150,7 @@
   void DidStopFlinging() override;
   void LayoutAndPaintAsync(base::OnceClosure callback) override;
   void CompositeAndReadbackAsync(
-      blink::WebCompositeAndReadbackAsyncCallback* callback) override;
+      base::OnceCallback<void(const SkBitmap&)> callback) override;
   void SynchronouslyCompositeNoRasterForTesting() override;
   void SetDeferCommits(bool defer_commits) override;
   void RegisterViewportLayers(