[Sync] Add histograms for sync response/error codes

sync/internal_api/http_bridge.cc

Index: sync/internal_api/http_bridge.cc
diff --git a/sync/internal_api/http_bridge.cc b/sync/internal_api/http_bridge.cc
index 6da0dd31e8538eac57c68e9f9202afe09ca9015b..68d2762f8d1fb6db0ec063e173d7c69333d16018 100644
--- a/sync/internal_api/http_bridge.cc
+++ b/sync/internal_api/http_bridge.cc
@@ -7,6 +7,7 @@
 #include "base/message_loop/message_loop.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram_macros.h"
+#include "base/metrics/sparse_histogram.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
@@ -432,6 +433,10 @@ void HttpBridge::OnURLFetchComplete(const net::URLFetcher* source) {
 
   if (fetch_state_.request_succeeded)
     LogTimeout(false);
+  UMA_HISTOGRAM_SPARSE_SLOWLY("Sync.URLFetchResponse",
+                              source->GetStatus().is_success()
+                                  ? source->GetResponseCode()
+                                  : source->GetStatus().ToNetError());
   UMA_HISTOGRAM_LONG_TIMES("Sync.URLFetchTime",
                            fetch_state_.end_time - fetch_state_.start_time);