Ryan Hunt 1c5e585bd6 Simplify copying the front buffer to the back buffer (bug 1399692 part 5, r=bas)
To sync the back buffer with the front buffer, we set the back buffer rect and
rotation to the front buffer's, and then copy over the pixels that different.

We used to do the updating of the rect and rotation before BeginPaint, but that
isn't necessary and we can move it to be with the copying of pixels.

MozReview-Commit-ID: HzBKvMZkn1

--HG--
extra : rebase_source : 053e55df273d0d89327b80bc599ee05a020f6fef
extra : intermediate-source : 467532fd5b7a2385ba0dbdb9201e28e8f2b4a583
extra : source : 3d0da65640964e5a0565b5e7b7646cf719ce1449
2017-10-23 18:27:53 -04:00
..