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 112 matching lines @@
     if (bytes_used >= min_log_bytes_ &&
         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;
   }
+  int dropped_logs_num = 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));
+      dropped_logs_num++;
       continue;
     }
     AppendBase64String(list_[i].compressed_log_data, list_value);
     AppendBase64String(list_[i].hash, list_value);
   }
+  if (dropped_logs_num > 0)
+    UMA_HISTOGRAM_COUNTS("UMA.UnSentLogs.Dropped", dropped_logs_num);
 }
 
 PersistedLogs::LogReadStatus PersistedLogs::ReadLogsFromPrefList(
     const base::ListValue& list_value) {
   if (list_value.empty())
     return MakeRecallStatusHistogram(LIST_EMPTY);
 
   // For each log, there's two entries in the list (the data and the hash).
   DCHECK_EQ(0U, list_value.GetSize() % 2);
   const size_t log_count = list_value.GetSize() / 2;
 
   // Resize |list_| ahead of time, so that values can be decoded directly into
   // the elements of the list.
   DCHECK(list_.empty());
   list_.resize(log_count);
 
   for (size_t i = 0; i < log_count; ++i) {
     if (!ReadBase64String(list_value, i * 2, &list_[i].compressed_log_data) ||
         !ReadBase64String(list_value, i * 2 + 1, &list_[i].hash)) {
       list_.clear();
       return MakeRecallStatusHistogram(LOG_STRING_CORRUPTION);
     }
   }
 
   return MakeRecallStatusHistogram(RECALL_SUCCESS);
 }
 
 }  // namespace metrics