Use local pages for webrtc telemetry tests.

tools/perf/page_sets/webrtc_cases/datachannel_files/ga.js

Index: tools/perf/page_sets/webrtc_cases/datachannel_files/ga.js
diff --git a/tools/perf/page_sets/webrtc_cases/datachannel_files/ga.js b/tools/perf/page_sets/webrtc_cases/datachannel_files/ga.js
new file mode 100644
index 0000000000000000000000000000000000000000..864b9b2738fe7eacbbdeb946f1a57d8b73aaa123
--- /dev/null
+++ b/tools/perf/page_sets/webrtc_cases/datachannel_files/ga.js
@@ -0,0 +1,7 @@
+(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
+  (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
+  m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
+})(window,document,'script','//www.google-analytics.com/analytics.js','ga');
+
+ga('create', 'UA-48530561-1', 'auto');
+ga('send', 'pageview');