Only discard for XP dstCopies if we have a coverage value.

Only discard for XP dstCopies if we have a coverage value.

TBR=bsalomon@google.com

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/c19cdc254cc08f334b00c3b9fdb703818c8ca681

[egdaniel, 2015-05-10 15:33:15]

egdaniel@google.com changed reviewers:
+ bsalomon@google.com, joshualitt@google.com

[egdaniel, 2015-05-10 15:33:16]

This fixes the bugs introduced to our bledning when I disabled the adv blend
mode stuff. It was having a weird interaction with our recent change to not
define coverage variable in shader if we weren't using it. However when doing
dst copies we would still end up looking coverage for our discard check, thus
the error.

[joshualitt, 2015-05-10 15:36:58]

On 2015/05/10 15:33:16, egdaniel wrote:
> This fixes the bugs introduced to our bledning when I disabled the adv blend
> mode stuff. It was having a weird interaction with our recent change to not
> define coverage variable in shader if we weren't using it. However when doing
> dst copies we would still end up looking coverage for our discard check, thus
> the error.

lgtm

[egdaniel, 2015-05-10 15:38:12]

The CQ bit was checked by egdaniel@google.com

[commit-bot: I haz the power, 2015-05-10 15:38:26]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1125283005/20001

[commit-bot: I haz the power, 2015-05-10 15:45:25]

Committed patchset #2 (id:20001) as
https://skia.googlesource.com/skia/+/c19cdc254cc08f334b00c3b9fdb703818c8ca681