Merge multiple histogram snapshots into single one for reporting.

base/metrics/histogram_snapshot_manager_unittest.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 "base/metrics/histogram_snapshot_manager.h"
 
 #include <string>
 #include <vector>
 
 #include "base/metrics/histogram_delta_serialization.h"
@@ skipping 87 matching lines @@
   histogram_snapshot_manager_.PrepareDeltas(
       StatisticsRecorder::begin(false), StatisticsRecorder::end(),
       HistogramBase::kNoFlags, HistogramBase::kUmaStabilityHistogramFlag);
 
   const std::vector<std::string>& histograms =
       histogram_flattener_delta_recorder_.GetRecordedDeltaHistogramNames();
   EXPECT_EQ(1U, histograms.size());
   EXPECT_EQ("UmaStabilityHistogram", histograms[0]);
 }
 
+TEST_F(HistogramSnapshotManagerTest, CheckMerge) {
+  UMA_HISTOGRAM_ENUMERATION("UmaHistogram", 1, 2);
+  UMA_STABILITY_HISTOGRAM_ENUMERATION("UmaStabilityHistogram", 1, 2);
+
+  base::HistogramBase* h1 = base::LinearHistogram::FactoryGet(
+      "UmaHistogram", 1, 2, 3, 0);
+  EXPECT_TRUE(h1);
+  base::HistogramBase* h2 = base::LinearHistogram::FactoryGet(
+      "UmaStabilityHistogram", 1, 2, 3, 0);
+  EXPECT_TRUE(h1);
+
+  histogram_snapshot_manager_.StartDeltas();
+  histogram_snapshot_manager_.PrepareDelta(h1);
+  histogram_snapshot_manager_.PrepareDelta(h1);
+  histogram_snapshot_manager_.PrepareDelta(h2);
+  histogram_snapshot_manager_.PrepareDelta(h2);
+  histogram_snapshot_manager_.PrepareDelta(h1);
+  histogram_snapshot_manager_.FinishDeltas();
+
+  const std::vector<std::string>& histograms =
+      histogram_flattener_delta_recorder_.GetRecordedDeltaHistogramNames();
+  EXPECT_EQ(2U, histograms.size());
+}
+
 }  // namespace base