[Favicon] Add new fallback icon rendering flow.

chrome/browser/ui/webui/favicon_source.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_UI_WEBUI_FAVICON_SOURCE_H_
 #define CHROME_BROWSER_UI_WEBUI_FAVICON_SOURCE_H_
 
 #include <map>
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "base/task/cancelable_task_tracker.h"
 #include "chrome/browser/favicon/favicon_service.h"
 #include "content/public/browser/url_data_source.h"
 #include "ui/gfx/favicon_size.h"
 
 class Profile;
 
 // FaviconSource is the gateway between network-level chrome:
 // requests for favicons and the history backend that serves these.
 //
 // Format:
-//   chrome://favicon/size&scalefactor/urlmodifier/url
+//   chrome://favicon/size&scalefactor/fallback&specs/urlmodifier/url
 // Some parameters are optional as described below. However, the order of the
 // parameters is not interchangeable.
 //
 // Parameter:
 //  'url'               Required
 //    Specifies the page URL of the requested favicon. If the 'urlmodifier'
 //    parameter is 'iconurl', the URL refers to the URL of the favicon image
 //    instead.
 //  'size&scalefactor'  Optional
 //    Values: ['largest', size/aa@bx/]
 //    'largest': Specifies that the largest available favicon is requested.
 //      Example: chrome://favicon/largest/http://www.google.com/
 //    'size/aa@bx/':
 //      Specifies the requested favicon's size in DIP (aa) and the requested
 //      favicon's scale factor. (b).
 //      The supported requested DIP sizes are: 16x16, 32x32 and 64x64.
 //      If the parameter is unspecified, the requested favicon's size defaults
 //      to 16 and the requested scale factor defaults to 1x.
 //      Example: chrome://favicon/size/16@2x/http://www.google.com/
-//  'urlmodifier'      Optional
+//  'fallback&specs'    Optional
+//    Values: ['fallback/<specs>/']
+//    'fallback/specs/':
+//      Specifies explicit request of a fallback favicon. <specs> is a comma-
+//      separated string of fallback specifications. For details, see
+//      /components/favicon_base/fallback_icon_specs_builder.h.
+//     Example: chrome://favicon/fallback/fff,000/http://www.google.com/
+//      This requests the fallback favicon for http://www.google.com, using
+//      #fff as the background color and #000 as the text color.
+//  'urlmodifier'       Optional
 //    Values: ['iconurl', 'origin']
 //    'iconurl': Specifies that the url parameter refers to the URL of
 //    the favicon image as opposed to the URL of the page that the favicon is
 //    on.
 //    Example: chrome://favicon/iconurl/http://www.google.com/favicon.ico
 //    'origin': Specifies that the URL should be converted to a form with
 //    an empty path and a valid scheme. The converted URL will be used to
 //    request the favicon from the favicon service.
 //    Examples:
 //      chrome://favicon/origin/http://example.com/a
@@ skipping 79 matching lines @@
   // database doesn't have a favicon for a webpage. Indexed by IconSize values.
   scoped_refptr<base::RefCountedMemory> default_favicons_[NUM_SIZES];
 
   // The favicon_base::IconTypes of icon that this FaviconSource handles.
   int icon_types_;
 
   DISALLOW_COPY_AND_ASSIGN(FaviconSource);
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_FAVICON_SOURCE_H_