Implement manifest icon downloader

chrome/browser/manifest/manifest_icon_downloader.h

+// Copyright 2015 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 CHROME_BROWSER_MANIFEST_MANIFEST_ICON_DOWNLOADER_H_
+#define CHROME_BROWSER_MANIFEST_MANIFEST_ICON_DOWNLOADER_H_
+
+#include "base/basictypes.h"
+#include "base/bind.h"
+#include "base/memory/ref_counted.h"
+#include "content/public/browser/web_contents_observer.h"
+#include "third_party/skia/include/core/SkBitmap.h"
+
+namespace content {
+class WebContents;
+}  // namespace content
+
+namespace gfx {
+class Size;
+} // namespace gfx
+
+class GURL;
+
+class ManifestIconDownloader
+    : public content::WebContentsObserver {
+ public:
+  using IconFetchCallback = base::Callback<void(const SkBitmap&)>;
+
+  explicit ManifestIconDownloader(content::WebContents* web_contents);
+  ~ManifestIconDownloader() override = default;
+
+  // Downloads the icon located at icon_url. If the file contains multiple icons
+  // then it attempts to pick the one closest in size bigger than or
+  // equal to ideal_icon_size_in_dp, taking into account the density of the
+  // device. If a bigger icon is chosen then ,the icon is scaled down to be
+  // equal to ideal_icon_size_in_dp.
+  // The boolean return value indicates if the download could be successfully
+  // started. If this is false then the callback will NOT be called.

[mlamouri (slow - plz ping), 2015/08/07 10:11:12]

Could you change the last two lines to:
Returns whether the download has started. It will return false if the current
context or information do not allow to download the image.

[Lalit Maganti, 2015/08/07 13:04:30]

Done.

+  bool Download(const GURL& icon_url,
+                int ideal_icon_size_in_dp,
+                const IconFetchCallback& callback);
+
+ private:
+  // Callback run after an attempt to download the manifest icon has been made.

[mlamouri (slow - plz ping), 2015/08/07 10:11:11]

nit: this comment is confusing because it might be interpreted as "callback is
run after the download starts" which isn't actually correct, right?

[Lalit Maganti, 2015/08/07 13:04:30]

Fixed.

+  static void OnIconFetched(const int ideal_icon_size_in_px,
+                            const IconFetchCallback& callback,
+                            int id,
+                            int http_status_code,
+                            const GURL& url,
+                            const std::vector<SkBitmap>& bitmaps,
+                            const std::vector<gfx::Size>& sizes);
+
+  static int FindClosestBitmapIndex(const int ideal_icon_size_in_px,
+                                    const std::vector<SkBitmap>& bitmaps);
+
+  friend class ManifestIconDownloaderTest;
+
+  DISALLOW_COPY_AND_ASSIGN(ManifestIconDownloader);
+};
+
+#endif  // CHROME_BROWSER_MANIFEST_MANIFEST_ICON_DOWNLOADER_H_