Add histograms for requests that were fetched successfully

components/data_reduction_proxy/core/browser/data_reduction_proxy_config.cc

Index: components/data_reduction_proxy/core/browser/data_reduction_proxy_config.cc
diff --git a/components/data_reduction_proxy/core/browser/data_reduction_proxy_config.cc b/components/data_reduction_proxy/core/browser/data_reduction_proxy_config.cc
index 820a184dff1f5b19d02ea8eba77c099dded1a465..781381f1c8df597edffdbe4a60ce8b2bd14d5f85 100644
--- a/components/data_reduction_proxy/core/browser/data_reduction_proxy_config.cc
+++ b/components/data_reduction_proxy/core/browser/data_reduction_proxy_config.cc
@@ -357,7 +357,7 @@ bool DataReductionProxyConfig::IsDataReductionProxy(
     if (proxy_info) {
       proxy_info->proxy_servers =
           std::vector<net::ProxyServer>(proxy_it, proxy_list.end());
-      proxy_info->is_fallback = (proxy_it != proxy_list.begin());
+      proxy_info->proxy_index = proxy_it - proxy_list.begin();

[sclittle, 2016/05/27 21:17:28]

nit: add a static_cast<size_t> here. (proxy_it - proxy_list.begin()) is a
ptrdiff_t, which is signed, not unsigned like a size_t. The only reason this
doesn't cause a compiler warning is because those warning were turned off as so
much code in chromium does these implicit signed/unsigned casts.

[tbansal1, 2016/05/27 22:35:11]

Done.

     }
     return true;
   }