Reland "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..bff9620cc14a39f066040e5eba078d5729f7965b
--- /dev/null
+++ b/base/test/histogram_recorder_unittest.cc
@@ -0,0 +1,41 @@
+// 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();

[lpromero, 2013/12/17 18:53:16]

HistogramRecorders are now globally initialized, before any test case can run.
The problem with the original CL was that HistogramRecorder where initialized to
late. This fix could also fix crbug.com/230534, mentioned in a comment in
spellcheck_host_metrics_unittest.cc.

+  }
+};
+
+TEST_F(HistogramRecorderTest, Scope) {
+  // Send a histogram before the creation of the recorder.

[ppi, 2013/12/19 16:57:27]

Should we say "Record" instead of "Send"?

[lpromero, 2013/12/20 11:53:44]

Done.

+  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());
+
+  // Send a histogram after the creation of the recorder.

[ppi, 2013/12/19 16:57:27]

Should we say "Record" instead of "Send"?

[lpromero, 2013/12/20 11:53:44]

Done.

+  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