Add a HistogramRecorder class and use cases.

base/test/histogram_recorder_unittest.cc

Index: base/test/histogram_recorder_unittest.cc
diff --git a/base/test/histogram_recorder_unittest.cc b/base/test/histogram_recorder_unittest.cc
new file mode 100644
index 0000000000000000000000000000000000000000..a69c6b04c87a0396b8f68c4d2349ed6aefdb1fa2
--- /dev/null
+++ b/base/test/histogram_recorder_unittest.cc
@@ -0,0 +1,34 @@
+// 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 {};
+
+TEST_F(HistogramRecorderTest, Scope) {
+  // Send a histogram before the creation of the recorder.
+  UMA_HISTOGRAM_BOOLEAN("Test", true);
+
+  HistogramRecorder recorder;
+
+  // Verify that no histogram is recorded.
+  EXPECT_FALSE(recorder.GetHistogramSamplesSinceCreation("Test"));
+
+  // Send a histogram after the creation of the recorder.
+  UMA_HISTOGRAM_BOOLEAN("Test", true);
+
+  // Verify that one histogram is recorded.
+  scoped_ptr<HistogramSamples> samples(
+      recorder.GetHistogramSamplesSinceCreation("Test"));
+  EXPECT_TRUE(samples);
+  EXPECT_EQ(1, samples->TotalCount());
+}
+
+}  // namespace base