Fix pointer formatting in devtools trace events

The pointer is now formatted in platform-independent way.

BUG=361045
R=alph@chromium.org

Review URL: https://codereview.chromium.org/254583003

git-svn-id: svn://svn.chromium.org/blink/trunk@172608 bbb929c8-8fbe-4397-9dbb-9b2b20218538