Support "shared" histograms between processes.

base/metrics/histogram_delta_serialization_unittest.cc

 // Copyright 2013 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 "base/metrics/histogram_delta_serialization.h"
 
 #include <vector>
 
 #include "base/metrics/histogram.h"
 #include "base/metrics/histogram_base.h"
 #include "base/metrics/statistics_recorder.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
 
 TEST(HistogramDeltaSerializationTest, DeserializeHistogramAndAddSamples) {
   StatisticsRecorder statistic_recorder;
   HistogramDeltaSerialization serializer("HistogramDeltaSerializationTest");
   std::vector<std::string> deltas;
   // Nothing was changed yet.
-  serializer.PrepareAndSerializeDeltas(&deltas);
+  serializer.PrepareAndSerializeDeltas(&deltas, true);
   EXPECT_TRUE(deltas.empty());
 
   HistogramBase* histogram = Histogram::FactoryGet(
       "TestHistogram", 1, 1000, 10, HistogramBase::kIPCSerializationSourceFlag);
   histogram->Add(1);
   histogram->Add(10);
   histogram->Add(100);
   histogram->Add(1000);
 
-  serializer.PrepareAndSerializeDeltas(&deltas);
+  serializer.PrepareAndSerializeDeltas(&deltas, true);
   EXPECT_FALSE(deltas.empty());
 
   HistogramDeltaSerialization::DeserializeAndAddSamples(deltas);
 
   // The histogram has kIPCSerializationSourceFlag. So samples will be ignored.
   scoped_ptr<HistogramSamples> snapshot(histogram->SnapshotSamples());
   EXPECT_EQ(1, snapshot->GetCount(1));
   EXPECT_EQ(1, snapshot->GetCount(10));
   EXPECT_EQ(1, snapshot->GetCount(100));
   EXPECT_EQ(1, snapshot->GetCount(1000));
 
   // Clear kIPCSerializationSourceFlag to emulate multi-process usage.
   histogram->ClearFlags(HistogramBase::kIPCSerializationSourceFlag);
   HistogramDeltaSerialization::DeserializeAndAddSamples(deltas);
 
   scoped_ptr<HistogramSamples> snapshot2(histogram->SnapshotSamples());
   EXPECT_EQ(2, snapshot2->GetCount(1));
   EXPECT_EQ(2, snapshot2->GetCount(10));
   EXPECT_EQ(2, snapshot2->GetCount(100));
   EXPECT_EQ(2, snapshot2->GetCount(1000));
 }
 
 }  // namespace base