Faster request body verification in XHR send handler
Faster request body verification in XHR send handler

This fixes the performance bottleneck of XHR send benchmarking.

R=tyoshino@chromium.org

Review URL: https://codereview.appspot.com/131350043
GoogleChromeLabs/pywebsocket3,google/pywebsocket,GoogleChromeLabs/pywebsocket3,google/pywebsocket,GoogleChromeLabs/pywebsocket3,google/pywebsocket,googlearchive/pywebsocket,googlearchive/pywebsocket,googlearchive/pywebsocket