There has always been code that should abide by the web development
style guide[1] in ui/webui/ but hasn't been automatedly checked.

Additionally, code from chrome/browser/ was moved to
components/flags_ui/, components/version_ui/, components/about_ui/ a
while ago to be used on iOS and was previously checked by presubmits but
is no longer.

This CL moves web_dev_style to a more generic location and hopefully
makes it easier to check a whole CL's web resources with a single method
call.

R=tsergeant@chromium.org
BUG=723234
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2890513003
Cr-Commit-Position: refs/heads/master@{#472588}