Added UMA metrics for MediaSourcePlayer and MediaCodecPlayer

media/base/android/media_statistics.h

+// Copyright 2015 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 MEDIA_BASE_ANDROID_MEDIA_STATISTICS_H_
+#define MEDIA_BASE_ANDROID_MEDIA_STATISTICS_H_
+
+#include <stdint.h>
+#include "base/time/time.h"
+#include "media/base/demuxer_stream.h"
+
+namespace media {
+
+// FrameStatistics struct deals with frames of one stream, i.e. either
+// audio or video.
+struct FrameStatistics {
+  // Stream type that this statistics belong to (Audio or Video).
+  DemuxerStream::Type stream_type;
+
+  // Audio: total number of frame that has been rendered.

[Ilya Sherman, 2015/10/01 07:19:20]

nit: "has" -> "have"

[Tima Vaisburd, 2015/10/01 20:05:16]

Done.

+  // Video: total amount of frames thatwere supposed to be rendered. Late video

[Ilya Sherman, 2015/10/01 07:19:20]

nit: "thatwere" -> "that were"

[Tima Vaisburd, 2015/10/01 20:05:16]

Done.

+  // frames might be skipped, but are counted here.
+  uint32_t total;
+
+  // A number of late frames. Late frames are a subset of the total frames.

[xhwang, 2015/09/30 21:02:58]

What's the definition of being late?

[Tima Vaisburd, 2015/10/01 20:05:15]

Copied the text from histogram.xml

+  uint32_t late;

[xhwang, 2015/09/30 21:02:57]

nit: consider using Non-Static Class Member Initializers:

https://chromium-cpp.appspot.com/

[Tima Vaisburd, 2015/10/01 20:05:15]

Done.

+
+  FrameStatistics(DemuxerStream::Type type)
+      : stream_type(type), total(0), late(0) {}
+
+  void Clear() { total = late = 0; }
+
+  // Adds a frame to |total|.
+  void AddFrame() { ++total; }
+
+  // Adds a frame to |late|. For each AddLateFrame() call there should be
+  // preceding AddFrame() call.
+  void AddLateFrame(base::TimeDelta delay);
+};
+
+// MediaStatistics class gathers and reports playback quality statistics to UMA.
+//
+// This class is not thread safe. The caller should guarantee that operations
+// on FrameStatistics objects does not happen during Start() and
+// StopAndReport(). The Start() and StopAndReport() methods need to be called
+// sequantially.
+
+class MediaStatistics {
+ public:
+  MediaStatistics();
+  ~MediaStatistics();
+
+  // Returns the frame statistics for audio frames.
+  FrameStatistics& audio_frames() { return audio_frames_; }

[xhwang, 2015/09/30 21:02:58]

nit: s/audio_frame/audio_frame_statistic 

[Tima Vaisburd, 2015/10/01 20:05:16]

The only place in the code it is being called has the form
media_stat_->audio_frames(), so it seems it's clear that it refers to statistics
about frames. What do you think?

+
+  // Returns the frame statistics for video frames.
+  FrameStatistics& video_frames() { return video_frames_; }

[xhwang, 2015/09/30 21:02:58]

ditto

[Tima Vaisburd, 2015/10/01 20:05:16]

See above

+
+  // Starts gathering statistics. Can be called several times in the row, the
+  // latest call takes effect.
+  void Start(base::TimeDelta current_playback_time);
+
+  // Stops gathering statistics, calculate and report results. Can be called
+  // several times in a row, without a prior Start() this call is ignored.
+  void StopAndReport(base::TimeDelta current_playback_time);

[xhwang, 2015/09/30 21:02:58]

When called in a row, will only the first call take effect?

[Tima Vaisburd, 2015/10/01 20:05:16]

This is what I wanted to say. Changed the comment.

+
+  // Adds starvation event.
+  void AddStarvation() { ++num_starvations_; }
+
+ private:
+  // Resets the data to the initial state.
+  void Clear();
+
+  // Calculates relative data based on total frame numbers and reports it and
+  // the duration to UMA.
+  void Report(base::TimeDelta duration);
+
+  base::TimeDelta start_time_;
+  FrameStatistics audio_frames_;
+  FrameStatistics video_frames_;
+  uint32_t num_starvations_;
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_ANDROID_MEDIA_STATISTICS_H_