impl: Make sure OzoneDisplay::spec_ is meant for browser UI only

Note that this patch and the previous fix the geometries of non-root windows.
So for instance, right-click in the address bar now open the cute menu as
expected.
impl: OzoneDisplay::OnChannelEstablished shouldn't send old and useless data

Once the channel is established, the browser process already has been running
for awhile and the output geometries in question were already accessed by the
UI. So it's just useless to dispatch a late OutputSizeChanged.