Make FaviconService::GetRawFaviconForPageURL() select the best candidate among all the icon types

components/history/core/browser/thumbnail_database.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 COMPONENTS_HISTORY_CORE_BROWSER_THUMBNAIL_DATABASE_H_
 #define COMPONENTS_HISTORY_CORE_BROWSER_THUMBNAIL_DATABASE_H_
 
 #include <vector>
 
 #include "base/gtest_prod_util.h"
@@ skipping 147 matching lines @@
   bool DeleteFavicon(favicon_base::FaviconID id);
 
   // Icon Mapping --------------------------------------------------------------
   //
   // Returns true if there is a matched icon mapping for the given page and
   // icon type.
   // The matched icon mapping is returned in the icon_mapping parameter if it is
   // not NULL.
 
   // Returns true if there are icon mappings for the given page and icon types.
-  // If |required_icon_types| contains multiple icon types and there is more
-  // than one matched icon type in the database, icons of only a single type
-  // will be returned in the priority of TOUCH_PRECOMPOSED_ICON, TOUCH_ICON,
-  // and FAVICON.
   // The matched icon mappings are returned in the |mapping_data| parameter if
   // it is not NULL.
   bool GetIconMappingsForPageURL(const GURL& page_url,
                                  int required_icon_types,
                                  std::vector<IconMapping>* mapping_data);
 
   // Returns true if there is any matched icon mapping for the given page.
   // All matched icon mappings are returned in descent order of IconType if
   // mapping_data is not NULL.

[mastiz, 2017/04/20 08:55:59]

Does anybody use the sorting per IconType? If not, update comment and simplify
SQL? This would otherwise remain is historic artifact.

[pkotwicz, 2017/04/30 03:49:56]

No, no one uses the sorting per IconType. It is useful though. For instance, if
there is a favicon of type FAVICON and a favicon of type TOUCH_ICON stored in
the database for the same page URL the sorting affects which of the two bitmaps
is returned. This makes the favicon logic more predictable which is good

   bool GetIconMappingsForPageURL(const GURL& page_url,
                                  std::vector<IconMapping>* mapping_data);
 
   // Adds a mapping between the given page_url and icon_id.
   // Returns the new mapping id if the adding succeeds, otherwise 0 is returned.
   IconMappingID AddIconMapping(const GURL& page_url,
                                favicon_base::FaviconID icon_id);
 
   // Deletes the icon mapping entries for the given page url.
   // Returns true if the deletion succeeded.
@@ skipping 76 matching lines @@
 
   sql::Connection db_;
   sql::MetaTable meta_table_;
 
   HistoryBackendClient* backend_client_;
 };
 
 }  // namespace history
 
 #endif  // COMPONENTS_HISTORY_CORE_BROWSER_THUMBNAIL_DATABASE_H_