Use hi-resolution favicon variants if available.

chrome/common/icon_messages.h

 // Copyright (c) 2011 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.
 
 // Multiply-included message file, no traditional include guard.
 #include <vector>
 
 #include "chrome/common/favicon_url.h"
 #include "ipc/ipc_message.h"
 #include "ipc/ipc_message_macros.h"
 #include "ipc/ipc_param_traits.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 
 #define IPC_MESSAGE_START IconMsgStart
 
 IPC_ENUM_TRAITS(FaviconURL::IconType)
 
 IPC_STRUCT_TRAITS_BEGIN(FaviconURL)
   IPC_STRUCT_TRAITS_MEMBER(icon_url)
   IPC_STRUCT_TRAITS_MEMBER(icon_type)
 IPC_STRUCT_TRAITS_END()
 
 // Messages sent from the browser to the renderer.
 
-// Requests the renderer to download the specified favicon image encode it as
-// PNG and send the PNG data back ala IconHostMsg_DidDownloadFavicon.
+// Requests the renderer to download the specified favicon image, decode it,
+// and send the image data back via IconHostMsg_DidDownloadFavicon.
 IPC_MESSAGE_ROUTED3(IconMsg_DownloadFavicon,
                     int /* identifier for the request */,
                     GURL /* URL of the image */,
-                    int /* Size of the image. Normally 0, but set if you have
-                           a preferred image size to request, such as when
-                           downloading the favicon */)
+                    int /* Preferred favicon size. Passed on to
+                           IconHostMsg_DidDownloadFavicon, unused otherwise */)
 
 // Messages sent from the renderer to the browser.
 
 // Notification that the urls for the favicon of a site has been determined.
 IPC_MESSAGE_ROUTED2(IconHostMsg_UpdateFaviconURL,
                     int32 /* page_id */,
                     std::vector<FaviconURL> /* urls of the favicon */)
 
-IPC_MESSAGE_ROUTED4(IconHostMsg_DidDownloadFavicon,
+IPC_MESSAGE_ROUTED5(IconHostMsg_DidDownloadFavicon,
                     int /* Identifier of the request */,
                     GURL /* URL of the image */,
                     bool /* true if there was a network error */,
-                    SkBitmap /* image_data */)
+                    int /* Preferred icon size passed to
+                           IconMsg_DownloadFavicon */,
+                    std::vector<SkBitmap> /* image_data */)