DevTools: Always show empty placeholder in ObjectPropertySection.

The placeholders are: "No Properties", "No Entries", "No Scopes", etc.
Right now we don't always show it, e.g. console.dir({ foo: { __proto__: null } })

Drive-by: pretty padding in tests with console.dir() and console.trace().

R=yurys

Review URL: https://codereview.chromium.org/575463002

git-svn-id: svn://svn.chromium.org/blink/trunk@182049 bbb929c8-8fbe-4397-9dbb-9b2b20218538