GitLab

Adds support in the content::URLDataSource for DOM Distiller for displaying
distilled articles.

Also adds preliminary error handling.

Depends on https://codereview.chromium.org/105723002/

BUG=319881

Review URL: https://codereview.chromium.org/134873008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247645 0039d316-1c4b-4281-b951-d872f2087c98