Add History.TopHostsVisitsByRank UMA metric.

components/history/core/browser/url_utils.cc

Index: components/history/core/browser/url_utils.cc
diff --git a/components/history/core/browser/url_utils.cc b/components/history/core/browser/url_utils.cc
index a993619be392f9d842a1a11a0647b0494dab4b54..a6e86c097eedfdcaa654800d1e9e1c5f52a379f4 100644
--- a/components/history/core/browser/url_utils.cc
+++ b/components/history/core/browser/url_utils.cc
@@ -6,6 +6,7 @@
 
 #include <algorithm>
 
+#include "base/strings/string_util.h"
 #include "url/gurl.h"
 
 namespace history {
@@ -85,4 +86,11 @@ GURL ToggleHTTPAndHTTPS(const GURL& url) {
   return url.ReplaceComponents(replacement);
 }
 
+std::string HostForTopHosts(const GURL& url) {
+  std::string host = url.host();
+  if (StartsWithASCII(host, "www.", true))
+    host.assign(host, 4, std::string::npos);

[sky, 2015/06/15 17:28:17]

nit: no need to reassign to host, just return the substring.

[twifkak, 2015/06/16 20:25:24]

Was trying to make use of NRVO. Returning just the substring here would break
NRVO, IIUC, and create an additional copy in the case where the host doesn't
start with "www.".

I mean, I don't have a benchmark for this, so I obviously don't have a strong
performance need. Also, it's entirely likely I'm wrong about the above. I'm
happy to change if you feel strongly.

+  return host;
+}
+
 }  // namespace history