Use local pages for webrtc telemetry tests.

tools/perf/page_sets/webrtc_cases/common.js

Index: tools/perf/page_sets/webrtc_cases/common.js
diff --git a/tools/perf/page_sets/webrtc_cases/common.js b/tools/perf/page_sets/webrtc_cases/common.js
new file mode 100644
index 0000000000000000000000000000000000000000..047a0000481aa76ff011aff8647183cfbffa7d8a
--- /dev/null
+++ b/tools/perf/page_sets/webrtc_cases/common.js
@@ -0,0 +1,12 @@
+/*
+ * Copyright 2017 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.
+ */
+ /* exported trace */
+
+// Logging utility function.
+function trace(arg) {
+  var now = (window.performance.now() / 1000).toFixed(3);
+  console.log(now + ': ', arg);
+}