Collapse contentInsets and View margins in Toolbars

As content insets are meant to help line up the edges of views with
the content in adjacent ViewGroups, collapse individual view margins
with the insets to preserve this property. Margins still define a
minimum spacing between adjacent sibling views or the edges of the
Toolbar container.

Bug 15328526

Change-Id: I786ccdbed6b40930250fa22e2a6d0376d759f2d2