Add UMA metrics and histograms for locally managed users.

chrome/browser/policy/url_blacklist_manager.h

Index: chrome/browser/policy/url_blacklist_manager.h
===================================================================
--- chrome/browser/policy/url_blacklist_manager.h	(revision 177135)
+++ chrome/browser/policy/url_blacklist_manager.h	(working copy)
@@ -49,6 +49,9 @@
   // Returns true if the URL is blocked.
   bool IsURLBlocked(const GURL& url) const;
 
+  // Returns the number of items in the list.
+  size_t Size() const;
+
   // Returns true if the URL has a standard scheme. Only URLs with standard
   // schemes are filtered.
   static bool HasStandardScheme(const GURL& url);