Timeline: skip low-level trace events in TracingTimelineModel

- pass filter of hidden record to TracingTimelineModel;
- introduce Array.prototype.toObjectKeys(), as we frequently want
    to build set-like objects from a list of keys;
- return hidden record filter, not an Object from TimelineUIUtils;

BUG=361045
R=yurys@chromium.org

Review URL: https://codereview.chromium.org/346523003

git-svn-id: svn://svn.chromium.org/blink/trunk@176851 bbb929c8-8fbe-4397-9dbb-9b2b20218538