Promises Panel for DevTools.

This depends on https://codereview.chromium.org/574353002/.

BUG=348919

Review URL: https://codereview.chromium.org/560393004

git-svn-id: svn://svn.chromium.org/blink/trunk@182413 bbb929c8-8fbe-4397-9dbb-9b2b20218538