DevTools: Add an option to capture stacks in promise pane.

Now we'll be able to collect stack traces on promise creation and settlement events,
and show them in a popover, similar to Network panel.

BUG=348919
R=apavlov, yurys, eustas

Review URL: https://codereview.chromium.org/791403002

git-svn-id: svn://svn.chromium.org/blink/trunk@187042 bbb929c8-8fbe-4397-9dbb-9b2b20218538