Update from https://crrev.com/333737

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 "base/metrics/sample_map.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
 namespace {
 
 TEST(SampleMapTest, AccumulateTest) {
   SampleMap samples;
 
   samples.Accumulate(1, 100);
   samples.Accumulate(2, 200);
@@ skipping 62 matching lines @@
   EXPECT_EQ(3, max);
   EXPECT_EQ(200, count);
 
   it->Next();
   it->Get(&min, &max, &count);
   EXPECT_EQ(4, min);
   EXPECT_EQ(5, max);
   EXPECT_EQ(-300, count);
 
   it->Next();
+  EXPECT_TRUE(it->Done());
+}
+
+TEST(SampleMapIteratorTest, SkipEmptyRanges) {
+  SampleMap samples;
+  samples.Accumulate(5, 1);
+  samples.Accumulate(10, 2);
+  samples.Accumulate(15, 3);
+  samples.Accumulate(20, 4);
+  samples.Accumulate(25, 5);
+
+  SampleMap samples2;
+  samples2.Accumulate(5, 1);
+  samples2.Accumulate(20, 4);
+  samples2.Accumulate(25, 5);
+
+  samples.Subtract(samples2);
+
+  scoped_ptr<SampleCountIterator> it = samples.Iterator();
+  EXPECT_FALSE(it->Done());
+
+  HistogramBase::Sample min;
+  HistogramBase::Sample max;
+  HistogramBase::Count count;
+
   it->Get(&min, &max, &count);
-  EXPECT_EQ(5, min);
-  EXPECT_EQ(6, max);
-  EXPECT_EQ(0, count);
+  EXPECT_EQ(10, min);
+  EXPECT_EQ(11, max);
+  EXPECT_EQ(2, count);
+
+  it->Next();
+  EXPECT_FALSE(it->Done());
+
+  it->Get(&min, &max, &count);
+  EXPECT_EQ(15, min);
+  EXPECT_EQ(16, max);
+  EXPECT_EQ(3, count);
 
   it->Next();
   EXPECT_TRUE(it->Done());
 }
 
 #if (!defined(NDEBUG) || defined(DCHECK_ALWAYS_ON)) && GTEST_HAS_DEATH_TEST
 
 TEST(SampleMapIteratorDeathTest, IterateDoneTest) {
   SampleMap samples;
 
@@ skipping 11 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