TimelinePanel: move TimelineDetailView from TimelineView to TimelinePanel.

no business logic changes

BUG=316167
R=pfeldman@chromium.org

Review URL: https://codereview.chromium.org/163563002

git-svn-id: svn://svn.chromium.org/blink/trunk@167173 bbb929c8-8fbe-4397-9dbb-9b2b20218538