Fix a crash in the code which attempts to append the user agent to the list of outgoing headers in ChromeFrame sub requests. The crash occurs because the current headers passed in the BeginningTransaction are NULL.
Fix a crash in the code which attempts to append the user agent to the list of outgoing
headers in ChromeFrame sub requests. The crash occurs because the current headers passed
in the BeginningTransaction are NULL.

Fixes bug http://code.google.com/p/chromium/issues/detail?id=62853

Bug=62853

Review URL: http://codereview.chromium.org/4792002

git-svn-id: http://src.chromium.org/svn/trunk/src@65834 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 0384347383c07deede1752f19c1196ff5d4309d5
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser