support content_shell

chromium content_shell for linux uses different version string.
this string is fixed and it's not updated automatically.
('content_shell_version': '19.77.34.5') in content_shell.gypi
if the browser is content_shell, the version will have '77.34.5' delimiter.
so we can support content_shell to use tracing by checking the delimiter.

BUG=674
Merge pull request #680 from fnwinter/support_content_shell

support content_shell