Disable check-webkit-style for Jinja templates

Jinja templates generally use the same extension as their output file,
but contain template code which the style checker can't understand.
(...and thus presubmit checks fail)
This adds a setting in the usual path-specific filters section to not
check these paths.

This is in response to an issue raised by Alan:
https://codereview.chromium.org/21006006/#msg8

Review URL: https://chromiumcodereview.appspot.com/22514002

git-svn-id: svn://svn.chromium.org/blink/trunk@155663 bbb929c8-8fbe-4397-9dbb-9b2b20218538