Fix overflow bug in histogram sample data structures

base/metrics/sample_map_unittest.cc

 // Copyright (c) 2012 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/sample_map.h"
 
 #include "base/memory/scoped_ptr.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
 namespace {
 
 TEST(SampleMapTest, AccumulateTest) {
   SampleMap samples(1);
 
   samples.Accumulate(1, 100);
   samples.Accumulate(2, 200);
   samples.Accumulate(1, -200);
   EXPECT_EQ(-100, samples.GetCount(1));
   EXPECT_EQ(200, samples.GetCount(2));
 
   EXPECT_EQ(300, samples.sum());
   EXPECT_EQ(100, samples.TotalCount());
   EXPECT_EQ(samples.redundant_count(), samples.TotalCount());
 }
 
+TEST(SampleMapTest, Accumulate_LargeValuesDontOverflow) {
+  SampleMap samples(1);
+
+  samples.Accumulate(250000000, 100);
+  samples.Accumulate(500000000, 200);
+  samples.Accumulate(250000000, -200);
+  EXPECT_EQ(-100, samples.GetCount(250000000));
+  EXPECT_EQ(200, samples.GetCount(500000000));
+
+  EXPECT_EQ(75000000000LL, samples.sum());
+  EXPECT_EQ(100, samples.TotalCount());
+  EXPECT_EQ(samples.redundant_count(), samples.TotalCount());
+}
+
 TEST(SampleMapTest, AddSubtractTest) {
   SampleMap samples1(1);
   SampleMap samples2(2);
 
   samples1.Accumulate(1, 100);
   samples1.Accumulate(2, 100);
   samples1.Accumulate(3, 100);
 
   samples2.Accumulate(1, 200);
   samples2.Accumulate(2, 200);
@@ skipping 111 matching lines @@
   samples.Accumulate(1, 100);
   it = samples.Iterator();
   EXPECT_FALSE(it->Done());
 }
 
 #endif
 // (!defined(NDEBUG) || defined(DCHECK_ALWAYS_ON)) && GTEST_HAS_DEATH_TEST
 
 }  // namespace
 }  // namespace base