DevTools: Show preview in console of ES6 Map, Set, WeakMap and WeakSet entries.

BUG=376196
R=yurys, vsevik

Review URL: https://codereview.chromium.org/512003003

git-svn-id: svn://svn.chromium.org/blink/trunk@181972 bbb929c8-8fbe-4397-9dbb-9b2b20218538