Ensure PopularSite icon availability in ntp_tiles.

components/ntp_tiles/icon_cacher.h

Index: components/ntp_tiles/icon_cacher.h
diff --git a/components/ntp_tiles/icon_cacher.h b/components/ntp_tiles/icon_cacher.h
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+// 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 COMPONENTS_NTP_TILES_ICON_CACHER_H_
+#define COMPONENTS_NTP_TILES_ICON_CACHER_H_
+
+#include <memory>
+
+#include "base/callback.h"
+#include "base/memory/weak_ptr.h"
+#include "base/task/cancelable_task_tracker.h"
+#include "components/ntp_tiles/popular_sites.h"
+
+namespace favicon {
+class FaviconService;
+}  // namespace favicon
+
+namespace favicon_base {
+struct FaviconImageResult;
+}  // namespace favicon_base
+
+namespace gfx {
+class Image;
+}  // namespace gfx
+
+namespace image_fetcher {
+class ImageFetcher;
+}  // namespace image_fetcher
+
+namespace ntp_tiles {
+
+// Ensures that a Popular Sites icon is cached, downloading and saving it if
+// not.
+//
+// Does not provide any way to get a fetched favicon; use the FaviconService for
+// that. All this class does is guarantee that FaviconService will be able to
+// get you an icon (if it exists).
+class IconCacher {
+ public:
+  IconCacher(favicon::FaviconService* favicon_service,
+             std::unique_ptr<image_fetcher::ImageFetcher> image_fetcher);
+  ~IconCacher();
+
+  // Fetches the icon if necessary, then invokes |done| with true if it was
+  // newly fetched (false if it was already cached or could not be fetched).
+  void StartFetch(PopularSites::Site site,
+                  const base::Callback<void(bool)>& done);
+
+ private:
+  void OnGetFaviconImageForPageURLFinished(
+      PopularSites::Site site,
+      const base::Callback<void(bool)>& done,
+      const favicon_base::FaviconImageResult& result);
+
+  void OnFaviconDownloaded(PopularSites::Site site,
+                           const base::Callback<void(bool)>& done,
+                           const std::string& id,
+                           const gfx::Image& fetched_image);
+
+  base::CancelableTaskTracker tracker_;
+  favicon::FaviconService* const favicon_service_;
+  std::unique_ptr<image_fetcher::ImageFetcher> const image_fetcher_;
+
+  DISALLOW_COPY_AND_ASSIGN(IconCacher);
+};
+
+}  // namespace ntp_tiles
+
+#endif  // COMPONENTS_NTP_TILES_ICON_CACHER_H_