Create a ClipArea class to handle tracking clip regions. This class can
select the most efficient implementation depending on the types of
clipping presented.
ClipArea re-used the rectangle and region-based clipping
implementations as well as adding a "list of rotated rectangles"
approach that is more efficient for rotated views with children.
Change-Id: I2133761a2462ebc0852b394220e265974b3086f0
Adds remaining missing overrides and nullptr usages, missed due to
an extreme failure in tool usage.
Change-Id: I56abd72975a3999ad13330003c348db40f59aebf
