[Favicon] Add new fallback icon rendering flow.

chrome/common/favicon/fallback_icon_url_parser.h

+// Copyright 2015 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_COMMON_FAVICON_FALLBACK_ICON_URL_PARSER_H_
+#define CHROME_COMMON_FAVICON_FALLBACK_ICON_URL_PARSER_H_
+
+#include <string>
+
+#include "components/favicon_base/fallback_icon_style_builder.h"
+
+namespace chrome {
+
+struct ParsedFallbackIconPath {
+  // The URL from which the fallback icon is being requested.
+  std::string url;
+
+  // The size of the requested fallback icon in dip.
+  int size_in_dip;
+
+  // The device scale factor of the requested fallback icon.
+  float device_scale_factor;
+
+  // Specifications of fallback icon. This is nullptr if no fallback.
+  favicon_base::FallbackIconStyleBuilder style_builder;
+};
+
+// Parses |path|,which should be in the format described at the top of the
+// file "chrome/browser/ui/webui/fallback_icon_source.h".
+bool ParseFallbackIconPath(const std::string& path,
+                           ParsedFallbackIconPath* parsed);
+
+}  // namespace chrome
+
+#endif  // CHROME_COMMON_FAVICON_FALLBACK_ICON_URL_PARSER_H_