FlameChart: replace entryOffsets with entryStartTimes

BUG=372190

Review URL: https://codereview.chromium.org/283333003

git-svn-id: svn://svn.chromium.org/blink/trunk@174093 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Support warning decorations in Timeline flame chart based on trace events

BUG=361045

Review URL: https://codereview.chromium.org/286123002

git-svn-id: svn://svn.chromium.org/blink/trunk@174094 bbb929c8-8fbe-4397-9dbb-9b2b20218538