Timeline: FilterBar prepared for dynamicaly updating set of filters.

BTW: One method was misplaced.

BUG=
R=caseq@chromium.org

Review URL: https://codereview.chromium.org/115133002

git-svn-id: svn://svn.chromium.org/blink/trunk@163861 bbb929c8-8fbe-4397-9dbb-9b2b20218538