Fix overflow bug in histogram sample data structures

base/metrics/sparse_histogram_unittest.cc

Index: base/metrics/sparse_histogram_unittest.cc
diff --git a/base/metrics/sparse_histogram_unittest.cc b/base/metrics/sparse_histogram_unittest.cc
index 83cf5d372472fd25161f7bd725d5f0a152bff126..619f42f6c572fb99031b4031fdc08480bb221206 100644
--- a/base/metrics/sparse_histogram_unittest.cc
+++ b/base/metrics/sparse_histogram_unittest.cc
@@ -81,6 +81,26 @@ TEST_F(SparseHistogramTest, BasicTestAddCount) {
   EXPECT_EQ(25, snapshot2->GetCount(101));
 }
 
+TEST_F(SparseHistogramTest, LargeTestAddCount) {
+  scoped_ptr<SparseHistogram> histogram(NewSparseHistogram("Sparse"));
+  scoped_ptr<HistogramSamples> snapshot(histogram->SnapshotSamples());
+  EXPECT_EQ(0, snapshot->TotalCount());
+  EXPECT_EQ(0, snapshot->sum());
+
+  histogram->AddCount(1000000000, 15);
+  scoped_ptr<HistogramSamples> snapshot1(histogram->SnapshotSamples());
+  EXPECT_EQ(15, snapshot1->TotalCount());
+  EXPECT_EQ(15, snapshot1->GetCount(1000000000));
+
+  histogram->AddCount(1000000000, 15);
+  histogram->AddCount(1010000000, 25);
+  scoped_ptr<HistogramSamples> snapshot2(histogram->SnapshotSamples());
+  EXPECT_EQ(55, snapshot2->TotalCount());
+  EXPECT_EQ(30, snapshot2->GetCount(1000000000));
+  EXPECT_EQ(25, snapshot2->GetCount(1010000000));
+  EXPECT_EQ(55250000000LL, snapshot2->sum());
+}
+
 TEST_F(SparseHistogramTest, MacroBasicTest) {
   UMA_HISTOGRAM_SPARSE_SLOWLY("Sparse", 100);
   UMA_HISTOGRAM_SPARSE_SLOWLY("Sparse", 200);