Timeline: replace showAggregatedStatsInDetails with a more generic showInDetails

This lets timeline views that don't operate on timeline records to display details.

BUG=

Review URL: https://codereview.chromium.org/219363002

git-svn-id: svn://svn.chromium.org/blink/trunk@170463 bbb929c8-8fbe-4397-9dbb-9b2b20218538