Add histograms for observing UMA throttling effect.

components/metrics/persisted_logs.cc

 // Copyright 2014 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.
 
 #include "components/metrics/persisted_logs.h"
 
 #include <string>
 
 #include "base/base64.h"
 #include "base/md5.h"
@@ skipping 113 matching lines @@
         saved_log_count >= min_log_count_) {
       break;
     }
     // Oversized logs won't be persisted, so don't count them.
     if (log_size > max_log_size_)
       continue;
     bytes_used += log_size;
     ++saved_log_count;
   }
 
+  UMA_HISTOGRAM_COUNTS("UMA.UnSentLog.Dropped", start - 1);
+
   for (size_t i = start; i < list_.size(); ++i) {
     size_t log_size = list_[i].compressed_log_data.length();
     if (log_size > max_log_size_) {
       UMA_HISTOGRAM_COUNTS("UMA.Large Accumulated Log Not Persisted",
                            static_cast<int>(log_size));
+      UMA_HISTOGRAM_COUNTS("UMA.UnSentLog.Dropped", 1);

[Alexei Svitkine (slow), 2016/04/08 15:08:32]

Can you just log the total at the end of the function? Otherwise, it's strange
to log a value of 1 here and some other value separately.

[gayane -on leave until 09-2017, 2016/04/08 17:19:25]

Done.

       continue;
     }
     AppendBase64String(list_[i].compressed_log_data, list_value);
     AppendBase64String(list_[i].hash, list_value);
   }
 }
 
 PersistedLogs::LogReadStatus PersistedLogs::ReadLogsFromPrefList(
     const base::ListValue& list_value) {
   if (list_value.empty())
@@ skipping 13 matching lines @@
         !ReadBase64String(list_value, i * 2 + 1, &list_[i].hash)) {
       list_.clear();
       return MakeRecallStatusHistogram(LOG_STRING_CORRUPTION);
     }
   }
 
   return MakeRecallStatusHistogram(RECALL_SUCCESS);
 }
 
 }  // namespace metrics