Support "shared" histograms between processes.

base/metrics/statistics_recorder_unittest.cc

Index: base/metrics/statistics_recorder_unittest.cc
diff --git a/base/metrics/statistics_recorder_unittest.cc b/base/metrics/statistics_recorder_unittest.cc
index 29caf49110d9c799a944f587a055a7b23b7da2c4..5c457d103916183773098b0af52aac24bcb394e6 100644
--- a/base/metrics/statistics_recorder_unittest.cc
+++ b/base/metrics/statistics_recorder_unittest.cc
@@ -23,7 +23,10 @@ class StatisticsRecorderTest : public testing::Test {
     InitializeStatisticsRecorder();
   }
 
-  void TearDown() override { UninitializeStatisticsRecorder(); }
+  void TearDown() override {
+    UninitializeStatisticsRecorder();
+    HistogramBase::SetDefaultPersistentMemoryAllocator(nullptr);
+  }
 
   void InitializeStatisticsRecorder() {
     statistics_recorder_ = new StatisticsRecorder();
@@ -313,6 +316,23 @@ TEST_F(StatisticsRecorderTest, ToJSON) {
   EXPECT_TRUE(json.empty());
 }
 
+TEST_F(StatisticsRecorderTest, IterationTest) {
+  StatisticsRecorder::Histograms registered_histograms;
+  LOCAL_HISTOGRAM_COUNTS("TestHistogram.IterationTest1", 30);
+  HistogramBase::SetDefaultPersistentMemoryAllocator(
+      new LocalPersistentMemoryAllocator(64 << 10, std::string()));
+  LOCAL_HISTOGRAM_COUNTS("TestHistogram.IterationTest2", 30);
+
+  StatisticsRecorder::HistogramIterator i1 = StatisticsRecorder::begin(true);
+  EXPECT_NE(StatisticsRecorder::end(), i1);
+  EXPECT_NE(StatisticsRecorder::end(), ++i1);
+  EXPECT_EQ(StatisticsRecorder::end(), ++i1);
+
+  StatisticsRecorder::HistogramIterator i2 = StatisticsRecorder::begin(false);
+  EXPECT_NE(StatisticsRecorder::end(), i2);
+  EXPECT_EQ(StatisticsRecorder::end(), ++i2);
+}
+
 namespace {
 
 // CallbackCheckWrapper is simply a convenient way to check and store that