DevTools: Update Properties sidebar pane on node changes.

Drive-by: Fix memleak because of a missing releaseObjectGroup() call.
Drive-by: Auto expand sections on updating or changing anchor node.

BUG=386407
R=vsevik, pfeldman

Review URL: https://codereview.chromium.org/581603002

git-svn-id: svn://svn.chromium.org/blink/trunk@182589 bbb929c8-8fbe-4397-9dbb-9b2b20218538