Support "shared" histograms between processes.

components/cronet/histogram_manager.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/cronet/histogram_manager.h"
 
 #include <string>
 #include <vector>
 
 #include "base/lazy_instance.h"
 #include "base/metrics/histogram.h"
 #include "base/metrics/histogram_samples.h"
+#include "base/metrics/statistics_recorder.h"
 #include "components/metrics/histogram_encoder.h"
 
 namespace cronet {
 
 // TODO(rtenneti): move g_histogram_manager into java code.
 static base::LazyInstance<HistogramManager>::Leaky
     g_histogram_manager = LAZY_INSTANCE_INITIALIZER;
 
 HistogramManager::HistogramManager() : histogram_snapshot_manager_(this) {
 }
@@ skipping 24 matching lines @@
 }
 
 void HistogramManager::InconsistencyDetectedInLoggedCount(int amount) {
   UMA_HISTOGRAM_COUNTS("Histogram.InconsistentSnapshotBrowser.Cronet",
                        std::abs(amount));
 }
 
 bool HistogramManager::GetDeltas(std::vector<uint8_t>* data) {
   // Clear the protobuf between calls.
   uma_proto_.Clear();
+  // "false" to StatisticsRecorder::begin() indicates to *not* include
+  // histograms held in persistent storage on the assumption that they will be
+  // visible to the recipient through other means.
   histogram_snapshot_manager_.PrepareDeltas(
+      base::StatisticsRecorder::begin(false), base::StatisticsRecorder::end(),
       base::Histogram::kNoFlags, base::Histogram::kUmaTargetedHistogramFlag);
   int32_t data_size = uma_proto_.ByteSize();
   data->resize(data_size);
   if (uma_proto_.SerializeToArray(&(*data)[0], data_size))
     return true;
   data->clear();
   return false;
 }
 
 }  // namespace cronet