[MD settings] clickable toggle labels on category default toggles

This CL makes top level category default rows react to mouse clicks.
These are the one or two rows at the top of a content settings category
(such as "cookies"). The rows are toggles. Before this CL the labels on
the toggles wouldn't act on mouse clicks when they should.

Also, there are several name changes and tiddying up that could be in a
separate CL if that is preferred.

BUG=704003
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2788853003
Cr-Commit-Position: refs/heads/master@{#461533}
2 files changed