Merge multiple histogram snapshots into single one for reporting.

base/metrics/histogram_snapshot_manager_unittest.cc

Index: base/metrics/histogram_snapshot_manager_unittest.cc
diff --git a/base/metrics/histogram_snapshot_manager_unittest.cc b/base/metrics/histogram_snapshot_manager_unittest.cc
index 20b324eb18fc107d0ce8a696064da5fb75d1ce5a..7e9021b00c4f76af7b18cfe7884d4c059817d0bd 100644
--- a/base/metrics/histogram_snapshot_manager_unittest.cc
+++ b/base/metrics/histogram_snapshot_manager_unittest.cc
@@ -105,4 +105,28 @@ TEST_F(HistogramSnapshotManagerTest,
   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