Attach mobile surface to the toolbar

Trevor promised to do this in Iafe64a6f but never did.

This needs styling changes to look right. It also means that
VE mobile standalone doesn't have a context at all right now,
which is horrible, but at least this makes MW mostly work.

Bug: 68546
Change-Id: Id8cc4b07905f777f667f36cbcc65e821847142d5
Merge "Attach mobile surface to the toolbar"