Use local pages for webrtc telemetry tests.

tools/perf/page_sets/webrtc_cases/datachannel_files/main(1).css

Index: tools/perf/page_sets/webrtc_cases/datachannel_files/main(1).css
diff --git a/tools/perf/page_sets/webrtc_cases/datachannel_files/main(1).css b/tools/perf/page_sets/webrtc_cases/datachannel_files/main(1).css
new file mode 100644
index 0000000000000000000000000000000000000000..e67dc1c1163a7e5c46b2fa255be4f755b9e05e09
--- /dev/null
+++ b/tools/perf/page_sets/webrtc_cases/datachannel_files/main(1).css
@@ -0,0 +1,24 @@
+/*
+ *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree.
+ */
+div.progress {
+  margin: 0 0 1em 0;
+}
+
+div.progress div.label {
+  display: inline-block;
+  font-weight: 400;
+  width: 8.2em;
+}
+
+div.input {
+  margin: 0 0 1em 0;
+}
+
+progress {
+  width: calc(100% - 8.5em);
+}