Track fraction of visits to top URLs.

chrome/browser/history/history_backend.h

Index: chrome/browser/history/history_backend.h
diff --git a/chrome/browser/history/history_backend.h b/chrome/browser/history/history_backend.h
index a55d6eb4b38e6613c2dff5c673b70e02e153a70f..cfda49c56a63a42c838a7a74d166a278cdc427ce 100644
--- a/chrome/browser/history/history_backend.h
+++ b/chrome/browser/history/history_backend.h
@@ -909,6 +909,12 @@ class HistoryBackend : public base::RefCountedThreadSafe<HistoryBackend>,
 #if defined(OS_ANDROID)
   // Used to provide the Android ContentProvider APIs.
   scoped_ptr<AndroidProviderBackend> android_provider_backend_;
+
+  // Used to provide UMA on the number of page visits that are to the most
+  // visited URLs. This is here because the backend both has access to this
+  // information and is notified of page visits. The top sites service should
+  // be used instead whenever possible.
+  MostVisitedURLList most_visited_urls_;
 #endif
 
   // Used to manage syncing of the typed urls datatype. This will be NULL