Add new PyAuto test for measuring audio tag latency.

chrome/test/functional/media/audio_latency_perf.py

+#!/usr/bin/env python
+# Copyright (c) 2012 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.
+
+"""Audio latency performance test.
+
+Benchmark measuring how fast we can continuously repeat a short sound clip.  In
+the ideal scenario we'd have zero latency processing script, seeking back to the
+beginning of the clip, and resuming audio playback.
+
+Performance is recorded as the average latency of N playbacks.  I.e., if we play
+a clip 50 times and the ideal duration of all playbacks is 1000ms and the total
+duration is 1500ms, the recorded result is (1500ms - 1000ms) / 50 == 10ms.
+"""
+import os
+
+import pyauto_media
+import pyauto_utils
+import pyauto
+
+
+# HTML test path; relative to src/chrome/test/data.
+_TEST_HTML_PATH = os.path.join('media', 'html', 'audio_latency_perf.html')
+
+
+class AudioLatencyPerfTest(pyauto.PyUITest):
+  """PyAuto test container.  See file doc string for more information."""
+
+  def testAudioLatency(self):
+    """Launches HTML test which runs the audio latency test."""
+    self.NavigateToURL(self.GetFileURLForDataPath(_TEST_HTML_PATH))
+
+    # Block until the test finishes and notifies us.
+    self.assertTrue(self.ExecuteJavascript('startTest(true);'))
+    ideal_duration = int(self.GetDOMValue('idealDuration'))
+    actual_duration = int(self.GetDOMValue('actualDuration'))
+    loop_count = int(self.GetDOMValue('loopCount'))
+
+    latency = float(actual_duration - ideal_duration) / loop_count

[shadi, 2012/05/17 22:03:37]

Is there a preference for calculating this here rather on the html page? (and
displaying it on the page as well)

[DaleCurtis, 2012/05/18 00:23:36]

Good point. I'll move the calculation into the page.

+    pyauto_utils.PrintPerfResult('audio_latency', 'latency', latency, 'ms')

[shadi, 2012/05/17 22:03:37]

Is the plan to just test the .wav file? If we want to later add ogg and mp3,
maybe it is better to pass the file names as params from the test.

Also, if that's the case I suggest adding the file name (or part of it) to the
graph name. 

[DaleCurtis, 2012/05/18 00:23:36]

No, just the wav file, test should be format agnostic. 

+
+
+if __name__ == '__main__':
+  pyauto_media.Main()