Reland "Add a HistogramRecorder class and use cases."

base/test/histogram_recorder_unittest.cc

+// Copyright 2013 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/memory/scoped_ptr.h"
+#include "base/metrics/histogram.h"
+#include "base/metrics/histogram_samples.h"
+#include "base/test/histogram_recorder.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace base {
+
+class HistogramRecorderTest : public testing::Test {
+ public:
+  static void SetUpTestCase() {
+    HistogramRecorder::Initialize();
+  }
+};
+
+TEST_F(HistogramRecorderTest, Scope) {
+  // Record a histogram before the creation of the recorder.
+  UMA_HISTOGRAM_BOOLEAN("Test", true);
+
+  HistogramRecorder recorder;
+
+  // Verify that no histogram is recorded.
+  scoped_ptr<HistogramSamples> samples(
+      recorder.GetHistogramSamplesSinceCreation("Test"));
+  EXPECT_TRUE(samples);
+  EXPECT_EQ(0, samples->TotalCount());
+
+  // Record a histogram after the creation of the recorder.
+  UMA_HISTOGRAM_BOOLEAN("Test", true);
+
+  // Verify that one histogram is recorded.
+  samples = recorder.GetHistogramSamplesSinceCreation("Test");
+  EXPECT_TRUE(samples);
+  EXPECT_EQ(1, samples->TotalCount());
+}
+
+}  // namespace base