DevTools Timeline: simulate sync Time record for Time/TimeEnd pair issued synchronously

This drops old logic that artificially glued Time/TimeEnd and re-parented them to root
and replaces it with insertion of synthetic sync Time records when Time/TimeEnd pair is encountered
on the same stack level (i.e. as siblings).
Drive-by: dump more record details in tests.

BUG=310430
R=pfeldman@chromium.org

Review URL: https://codereview.chromium.org/40563002

git-svn-id: svn://svn.chromium.org/blink/trunk@160831 bbb929c8-8fbe-4397-9dbb-9b2b20218538