Debug UI for DOM distiller supports distillation and lists articles.

This adds functionality to trigger distillation of web pages from the
debug UI and also lists the current set of articles.

BUG=319881

Review URL: https://codereview.chromium.org/105623002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239168 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239168