Implements peer connection stats measurements in WebRTC call test.

tools/perf/page_sets/webrtc_track_peerconnections.js

+// 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.
+
+// This file overwrites the webkitRTCPeerConnection constructor with a
+// new constructor which tracks all created connections. It does this by
+// periodically gathering statistics on all connections, using the WebRTC
+// statistics API. All reports are gathered into window.peerConnectionReports,
+// which contains one list per connection. In each list there is a number of
+// report batches, which in turn contains metric names mapped to values.
+
+window.peerConnectionReports = [];
+
+webkitRTCPeerConnection = (function() {
+  function getReportsAsDicts(getStatsResult) {
+    var result = [];
+    getStatsResult.forEach(function(report) {
+      var values = {};
+      report.names().forEach(function(name) {
+        values[name] = report.stat(name);
+      });
+      result.push(values);
+    });
+    return result;
+  }
+
+  function gatherStatsFromOneConnection(peerConnection) {
+    var connectionId = window.peerConnectionReports.length;
+    window.peerConnectionReports.push([]);
+    var pollIntervalMs = 1000;
+
+    setInterval(function() {
+      peerConnection.getStats(function(response) {
+        var reports = getReportsAsDicts(response.result());
+        window.peerConnectionReports[connectionId].push(reports);
+      });
+    }, pollIntervalMs);
+  }
+
+  var originalConstructor = webkitRTCPeerConnection;
+  return function() {
+    // Bind the incoming arguments to the original constructor.
+    var args = [null].concat(Array.prototype.slice.call(arguments));
+    var factoryFunction = originalConstructor.bind.apply(
+      originalConstructor, args);
+
+    // Create the object and track it.
+    var peerConnection = new factoryFunction();
+    gatherStatsFromOneConnection(peerConnection);
+    return peerConnection;
+  }
+})();