Revert of Revert of Move DstCopy on gpu into the GrXferProcessor.

Revert of Revert of Move DstCopy on gpu into the GrXferProcessor. (patchset #1 id:1 of https://codereview.chromium.org/901663007/)

Reason for revert:
The revert didn't help the 10.9 bot. Unreverting by reverting the revert (which is basically relanding the original patch which itself was a revert of a revert). Revert.

Original issue's description:
> Revert of Move DstCopy on gpu into the GrXferProcessor. (patchset #11 id:200001 of https://codereview.chromium.org/885923002/)
> 
> Reason for revert:
> Testing to see if reverting fixes 10.9 bots.
> 
> Original issue's description:
> > Move DstCopy on gpu into the GrXferProcessor.
> > 
> > BUG=skia:
> > 
> > Committed: https://skia.googlesource.com/skia/+/74a11753604768bf461b80cabb66060e8564d82c
> > 
> > Committed: https://skia.googlesource.com/skia/+/5e1378d0e075a323144ba14e0a4cbcca35eccc69
> 
> TBR=joshualitt@google.com,egdaniel@google.com
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=skia:
> 
> Committed: https://skia.googlesource.com/skia/+/21b2c53218ab25f4268e3992e51d916076a2a7ee

TBR=joshualitt@google.com,egdaniel@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Committed: https://skia.googlesource.com/skia/+/50785a3d10b53bea5beb6e18431a2449860be237

[bsalomon, 2015-02-06 15:01:52]

Created Revert of Revert of Move DstCopy on gpu into the GrXferProcessor.

[commit-bot: I haz the power, 2015-02-06 15:02:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/873723009/1

[commit-bot: I haz the power, 2015-02-06 15:02:42]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/50785a3d10b53bea5beb6e18431a2449860be237