DevTools: Wrong console preview for document.all property value.

This fixes wrong console output for "console.log({all: document.all})", namely:
- the property was shown as if it was "undefined"
- the preview was considered lossless, thus the object was not expandable

R=pfeldman, yurys

Review URL: https://codereview.chromium.org/83803002

git-svn-id: svn://svn.chromium.org/blink/trunk@162602 bbb929c8-8fbe-4397-9dbb-9b2b20218538