DevTools: Object accessors query results are to be shown as preview or array entry.

This is a follow-up to r160345, which made object accessors eval results
display as a preview instead of array entry. We should support both.

BUG=175898
R=pfeldman,vsevik

Review URL: https://codereview.chromium.org/38483006

git-svn-id: svn://svn.chromium.org/blink/trunk@160459 bbb929c8-8fbe-4397-9dbb-9b2b20218538