libvpx

Copy less when active map is in use

When active map is specified and the current frame is not a key frame,
golden frame nor a altref frame then copy only those active regions.

This significantly reduces encoding time by as much as 19% on the test
system where realtime encoding is used. This is particularly useful
when the frame size is large (e.g. 2560x1600) and there's only a few
action macroblocks.

Change-Id: If394a813ec2df5a0201745d1348dbde4278f7ad4