TimelinePanel: convert another portion of getters on TimelineModel.Record into functions

Mechanical change. No business logic changes.
thread, type, frameId, stackTrace and aggregatedStats were converted.

BUG=361045
R=yurys@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=172621

Review URL: https://codereview.chromium.org/251783002

git-svn-id: svn://svn.chromium.org/blink/trunk@172730 bbb929c8-8fbe-4397-9dbb-9b2b20218538