Consolidate serialization code in base::HistogramDeltasSerializer.

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);
+  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);
+  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