Add Net.ProxyScriptFetchSuccessDuration UMA to record how long PAC script fetches take.

net/proxy/proxy_script_fetcher_impl.h

 // Copyright (c) 2012 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 NET_PROXY_PROXY_SCRIPT_FETCHER_IMPL_H_
 #define NET_PROXY_PROXY_SCRIPT_FETCHER_IMPL_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 98 matching lines @@
   // This buffer is owned by the owner of |callback|, and will be filled with
   // UTF16 response on completion.
   base::string16* result_text_;
 
   // The maximum number of bytes to allow in responses.
   size_t max_response_bytes_;
 
   // The maximum amount of time to wait for download to complete.
   base::TimeDelta max_duration_;
 
+  // The time that the fetch started.
+  base::Time fetch_start_time_;
+
   // Factory for creating the time-out task. This takes care of revoking
   // outstanding tasks when |this| is deleted.
   base::WeakPtrFactory<ProxyScriptFetcherImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ProxyScriptFetcherImpl);
 };
 
 }  // namespace net
 
 #endif  // NET_PROXY_PROXY_SCRIPT_FETCHER_IMPL_H_