All functions do 2 pixels at a time.
90 and 270 rotations implemented.
YV16 refactored. YV12 code accepts a YuvType that allows the same code to support YV16 as well.
Special case for half size removed.
Special case for doubling added.  3.62 ms versus 8.62 for general purpose code.

Review URL: http://codereview.chromium.org/113407

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@16334 0039d316-1c4b-4281-b951-d872f2087c98