Timeline: make frames in TimelineView selectable

- generalize selection in timeline, so we can select multiple
    types of objects (currently, just records and frames);
- make frame bars in the top of classic Timeline view selectable
(mutually exclusive with selected records on the left);
- move contents of frame details popover into details view;

BUG=

Review URL: https://codereview.chromium.org/270693003

git-svn-id: svn://svn.chromium.org/blink/trunk@173656 bbb929c8-8fbe-4397-9dbb-9b2b20218538