DevTools: Show internal properties in object preview in console.

BUG=380312
R=yurys, pfeldman@chromium.org, amikhaylova@google.com

Review URL: https://codereview.chromium.org/317703003

git-svn-id: svn://svn.chromium.org/blink/trunk@175789 bbb929c8-8fbe-4397-9dbb-9b2b20218538