Ensure that favicons always have 1x representation regardless of whether the platform supports it

chrome/browser/favicon/favicon_util.h

 // Copyright (c) 2012 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_FAVICON_FAVICON_UTIL_H_
 #define CHROME_BROWSER_FAVICON_FAVICON_UTIL_H_
 
 #include "ui/base/layout.h"
 
 class GURL;
 
 namespace content {
 class RenderViewHost;
 }
 
 namespace gfx {
 class Image;
 }
 
 namespace history {
 struct FaviconBitmapResult;
 }
 
 // Utility class for common favicon related code.
 class FaviconUtil {
  public:
+  // Returns the scale factors at which favicons should be fetched. This is
+  // different from ui::GetSupportedScaleFactors() because clients which do
+  // not support 1x should still fetch a favicon for 1x to push to sync. This
+  // guarantees that the clients receiving sync updates pushed by this client
+  // receive a favicon (potentially of the wrong scale factor) and do not show
+  // the default favicon.
+  static std::vector<ui::ScaleFactor> GetFaviconScaleFactors();
+
   // Starts the download of the given favicon |url| from the given render view
   // host. When the download is finished, an IconHostMsg_DidDownloadFavicon IPC
   // message will be sent.
   // Returns the unique id of the download request. The id will be sent in the
   // IPC message.
   static int DownloadFavicon(content::RenderViewHost* rvh,
                              const GURL& url,
                              int image_size);
 
   // Takes a vector of png-encoded frames, decodes them, and converts them to
   // a favicon of size favicon_size (in DIPs) at the desired ui scale factors.
   static gfx::Image SelectFaviconFramesFromPNGs(
       const std::vector<history::FaviconBitmapResult>& png_data,
       const std::vector<ui::ScaleFactor> scale_factors,
       int favicon_size);
 };
 
 #endif  // CHROME_BROWSER_FAVICON_FAVICON_UTIL_H_