Extend LargeIconService to fetch missing favicons from a Google server

components/favicon/core/favicon_service.h

 // Copyright (c) 2017 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_FAVICON_CORE_FAVICON_SERVICE_H_
 #define COMPONENTS_FAVICON_CORE_FAVICON_SERVICE_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 171 matching lines @@
   // contains image reps for all of ui::GetSupportedScaleFactors(). Use
   // MergeFavicon() if it does not.
   // TODO(pkotwicz): Save unresized favicon bitmaps to the database.
   // TODO(pkotwicz): Support adding favicons for multiple icon URLs to the
   // thumbnail database.
   virtual void SetFavicons(const GURL& page_url,
                            const GURL& icon_url,
                            favicon_base::IconType icon_type,
                            const gfx::Image& image) = 0;
 
+  // Same as SetFavicons() with three differences:
+  // 1) It will be a no-op if there is an existing cached favicon for *any* type
+  //    for |page_url|.
+  // 2) If |icon_url| is known to the database, |bitmaps| will be ignored (i.e.
+  //    the icon won't be overwritten) but the mappings from |page_url| to
+  //    |icon_url| will be stored (conditioned to point 1 above).
+  // 3) If |icon_url| is stored, it will be marked as expired.
+  // The callback will receive whether the write actually happened.
+  virtual void SetLastResortFavicons(const GURL& page_url,
+                                     const GURL& icon_url,
+                                     favicon_base::IconType icon_type,
+                                     const gfx::Image& image,
+                                     base::Callback<void(bool)> callback) = 0;
+
   // Avoid repeated requests to download missing favicon.
   virtual void UnableToDownloadFavicon(const GURL& icon_url) = 0;
   virtual bool WasUnableToDownloadFavicon(const GURL& icon_url) const = 0;
   virtual void ClearUnableToDownloadFavicons() = 0;
 };
 
 }  // namespace favicon
 
 #endif  // COMPONENTS_FAVICON_CORE_FAVICON_SERVICE_H_