DevTools: Do not set distance to 0 for all objects held by global handles.

Only do so for Native Contexts that own user root objects.
The rest of objects should maintain their original distance from window.

R=yurys@chromium.org

Review URL: https://codereview.chromium.org/19971004

git-svn-id: svn://svn.chromium.org/blink/trunk@154749 bbb929c8-8fbe-4397-9dbb-9b2b20218538