In inline layout there's no need to do anything with overflow areas
since RelativePositionFrames handles it. Apparently doing some of the
work messes things up somehow, so the easy fix is to make the inline
::first-letter codepath behave more like nsInlineFrame and not do any
messing with overflow areas. So this moves the rest of the overflow
code in nsFirstLetterFrame::Reflow into the float-only codepath. There
don't appear to be any ordering issues with the movement, since the code
that the FinishAndStoreOverflow call is moved across deals with creating
and destroying continuations of the child.
All the added tests pass with the patch, but without the patch
overflow-inline-nooverflow.html fails.