DevTools: replace timeline GPUEvent 'ownerPID' with 'foreign'

The ownerPID property is too generic and there's no need exposing it
to the user. It has been replaced with the 'foreign' boolean
that shows if a gpu task is caused by the inspected renderer or not.

BUG=298951
R=pfeldman@chromium.org

Review URL: https://codereview.chromium.org/77433002

git-svn-id: svn://svn.chromium.org/blink/trunk@162375 bbb929c8-8fbe-4397-9dbb-9b2b20218538