[benchmark.html] Print time per message

R=ricea@chromium.org

Review URL: https://codereview.appspot.com/103110048

git-svn-id: http://pywebsocket.googlecode.com/svn/trunk@806 4ff78f4a-9131-11de-b045-6380ec9940d4
Add text mode to xhr_benchmark.html

R=yhirano@chromium.org, yhirano

Review URL: https://codereview.appspot.com/103170043

git-svn-id: http://pywebsocket.googlecode.com/svn/trunk@807 4ff78f4a-9131-11de-b045-6380ec9940d4