Revert 185318. It caused improvements in intl1/2 and morejs cyclers, but also

caused regressions in moz cycler tests. Perf data has been gathered, so the CL
is being reverted.

> Enable the threaded HTML parser by default
> 
> The threaded parser gets us to DOMContentLoaded about 10% faster on the telemetry top25 page set.  The threaded parser also reduces the maximum stop time due to parsing by 40% on the telemetry top25 page set.
> 
> Review URL: https://chromiumcodereview.appspot.com/12335103

TBR=abarth@chromium.org
Review URL: https://codereview.chromium.org/12380040

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@185352 0039d316-1c4b-4281-b951-d872f2087c98