Add History.TopHostsVisitsByRank UMA metric.

components/history/core/browser/url_utils.h

 // Copyright 2013 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_URL_UTILS_H_
 #define COMPONENTS_HISTORY_CORE_BROWSER_URL_UTILS_H_
 
 #include <string>
 
 class GURL;
@@ skipping 23 matching lines @@
 // Treats |path1| and |path2| as lists of path components (e.g., ["a", "bb"]
 // for "/a/bb"). Returns whether |path1|'s list is a prefix of |path2|'s list.
 // This is used to define "URL prefix". Note that "test" does not count as a
 // prefix of "testing", even though "test" is a (string) prefix of "testing".
 bool IsPathPrefix(const std::string& p1, const std::string& p2);
 
 // Converts |url| from HTTP to HTTPS, and vice versa, then returns the result.
 // If |url| is neither HTTP nor HTTPS, returns an empty URL.
 GURL ToggleHTTPAndHTTPS(const GURL& url);
 
+// Returns the host of the given URL, canonicalized as it would be for
+// HistoryService::TopHosts().
+std::string HostForTopHosts(const GURL& url);
+
 }  // namespace history
 
 #endif  // COMPONENTS_HISTORY_CORE_BROWSER_URL_UTILS_H_