Fix FloatingToolbar popup positioning.

The FloatingToolbar popup wrongly assumes that the main content panel
is wider than the overflow panel. In situations where this assumption
fails, the toolbar popup is positioned wrongly within it's container
window and items appear truncated. This CL fixes this issue.

Bug: 28550367
Change-Id: I41669b1deed7dd34f0b2bd060d14452482d3d36c
1 file changed