Reland "Add a HistogramRecorder class and use cases."

base/test/histogram_recorder.h

+// 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.
+
+#ifndef BASE_TEST_HISTOGRAM_RECORDER_H_
+#define BASE_TEST_HISTOGRAM_RECORDER_H_
+
+#include <map>
+
+#include "base/basictypes.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/metrics/histogram_samples.h"
+
+namespace base {
+
+// This class acts as a differential reader for histogram samples, enabling
+// tests to check that metrics were recorded as they should be.
+class HistogramRecorder {
+ public:
+  // Initializes the HistogramRecorder system.
+  static void Initialize();

[Mark Mentovai, 2013/12/20 18:07:12]

This shouldn’t precede the constructor.
http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml?showone=Declar...

[lpromero, 2013/12/20 18:22:42]

Done.

+  HistogramRecorder();
+  virtual ~HistogramRecorder();

[Mark Mentovai, 2013/12/20 18:07:12]

Why is this virtual? There are no other virtual methods here. This class is not
a base of any other class. This adds unnecessary indirection.

[lpromero, 2013/12/20 18:22:42]

Done.

+
+  // Returns whether the HistogramRecorder has been initialized.
+  static bool IsActive();
+
+  // Returns the histogram data accumulated since this instance was created.
+  // Returns NULL if no samples are available.
+  scoped_ptr<HistogramSamples> GetHistogramSamplesSinceCreation(
+      const std::string& histogram_name);
+
+ private:
+  // Used to determine the histogram changes made during this instance's
+  // lifecycle. This isntance takes ownership of the samples, which are deleted
+  // when the instance is destroyed.
+  std::map<std::string, HistogramSamples*> original_samples_;

[Mark Mentovai, 2013/12/20 18:07:12]

Include what you use: #include <string>

[lpromero, 2013/12/20 18:22:42]

Done.

+
+  DISALLOW_COPY_AND_ASSIGN(HistogramRecorder);
+};
+
+}  // namespace base
+
+#endif  // BASE_TEST_HISTOGRAM_RECORDER_H_