Implements peer connection stats measurements in WebRTC call test.

tools/perf/metrics/webrtc_stats.py

+# Copyright 2014 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.
+
+import json
+
+from metrics import Metric
+from telemetry.core import camel_case
+from telemetry.value import list_of_scalar_values
+
+INTERESTING_METRICS = {
+    'packetsReceived': {
+        'units': 'packets',
+        'description': 'Packets received by the peer connection',
+    },
+    'packetsSent': {
+        'units': 'packets',
+        'description': 'Packets sent by the peer connection',
+    },
+    'googDecodeMs': {
+        'units': 'ms',
+        'description': 'Time spent decoding.',
+    },
+    'googMaxDecodeMs': {
+        'units': 'ms',
+        'description': 'Maximum time spent decoding one frame.',
+    },
+    # TODO(phoglund): Add much more interesting metrics.
+}
+
+def SortStatsIntoTimeSeries(report_batches):
+  time_series = {}
+  for report_batch in report_batches:
+    for report in report_batch:
+      for stat_name, value in report.iteritems():
+        if stat_name not in INTERESTING_METRICS:
+          continue
+        time_series.setdefault(stat_name, []).append(float(value))
+
+  return time_series
+
+
+class WebRtcStatisticsMetric(Metric):
+  """Makes it possible to measure stats from peer connections."""
+
+  def __init__(self):
+    super(WebRtcStatisticsMetric, self).__init__()
+    self._all_reports = None
+
+  def Start(self, page, tab):
+    pass
+
+  def Stop(self, page, tab):
+    """Digs out stats from data populated by the javascript in webrtc_cases."""
+    self._all_reports = tab.EvaluateJavaScript(
+        'JSON.stringify(window.peerConnectionReports)')
+
+  def AddResults(self, tab, results):
+    if not self._all_reports:

[phoglund_chromium, 2014/10/01 13:17:45]

Actually, I ended up not logging or asserting here after all. My first solution
only loaded the tracking js if I expected the page to create peer connections.
Now it will always load the js, but it just won't do anything if no peer
connection are created. Thus, it seems reasonable to just return here if the
page didn't create any peer connections but just did getUserMedia and a local
stream.

+      return
+
+    reports = json.loads(self._all_reports)
+    for i, report in enumerate(reports):
+      time_series = SortStatsIntoTimeSeries(report)
+
+      for stat_name, values in time_series.iteritems():
+        stat_name_underscored = camel_case.ToUnderscore(stat_name)
+        trace_name = 'peer_connection_%d_%s' % (i, stat_name_underscored)
+        results.AddValue(list_of_scalar_values.ListOfScalarValues(
+            results.current_page, trace_name,
+            INTERESTING_METRICS[stat_name]['units'], values,
+            description=INTERESTING_METRICS[stat_name]['description'],
+            important=False))