Add devtools trace event for capturing current JS call stack

The event is controlled by a dedicated category and is off by default to not skew profile.

BUG=361045

Review URL: https://codereview.chromium.org/266913005

git-svn-id: svn://svn.chromium.org/blink/trunk@173311 bbb929c8-8fbe-4397-9dbb-9b2b20218538