Media Remoting: Draw remoting interstitial on poster image.

content/renderer/image_downloader/single_image_downloader.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CONTENT_RENDERER_IMAGE_DOWNLOADER_SINGLE_IMAGE_DOWNLOADER_H_
+#define CONTENT_RENDERER_IMAGE_DOWNLOADER_SINGLE_IMAGE_DOWNLOADER_H_
+
+#include "content/renderer/image_downloader/image_downloader_base.h"
+
+namespace content {
+
+// A one time image downloader that will download a single image. When there are
+// multiple frames, return the first one. Return an empty bitmap if downloading
+// fails.
+class SingleImageDownloader {
+ public:
+  using DownloadImageCallback = base::Callback<void(const SkBitmap&)>;
+
+  // Called to download the image in given |url|, and run |cb| when done.
+  // A new ImageDownloaderBase will be created and used to download the image,
+  // and will be destructed when downloading finishes or |render_frame| is
+  // destructed.
+  static void DownloadImage(RenderFrame* render_frame,

[miu, 2016/12/20 00:48:06]

Because the RenderFrame is used in a callback function, it feels like this
should be a WeakPtr<RenderFrame> here. (Just in case there are any weird
shutdown race conditions.) Then, inside this function, if the render_frame.get()
is null, run the DownloadImageCallback with an empty SkBitmap.

[xjz, 2016/12/20 21:46:25]

Done.

+                            const GURL& url,
+                            const DownloadImageCallback& cb);
+
+ private:
+  // Callback when downloading finishes.
+  static void DidDownloadImage(
+      std::unique_ptr<ImageDownloaderBase> image_downloader,
+      const DownloadImageCallback& callback,
+      int http_status_code,
+      const std::vector<SkBitmap>& images);
+
+  DISALLOW_COPY_AND_ASSIGN(SingleImageDownloader);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_IMAGE_DOWNLOADER_SINGLE_IMAGE_DOWNLOADER_H_