Add an InvariantOutput for the XPF.

Add an InvariantOutput for the XPF.

The Invariant output holds information about final post blended color and other
general information like will it blend with dst. Having this new struct allowed
me to also remove some functions that were previously querying subsets of the
invariant output.

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/9e4ecdc9f86724dcce23dc7546e2f295b901407b

[egdaniel, 2014-12-18 20:07:28]

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

[bsalomon, 2014-12-18 20:29:48]

lgtm

https://codereview.chromium.org/814933002/diff/1/src/gpu/effects/GrPorterDuff...
File src/gpu/effects/GrPorterDuffXferProcessor.cpp (right):

https://codereview.chromium.org/814933002/diff/1/src/gpu/effects/GrPorterDuff...
src/gpu/effects/GrPorterDuffXferProcessor.cpp:519: if ((!colorWriteDisabled &&
colorPOI.readsDst()) || coveragePOI.readsDst()) {
output->fWillBlendWithDst = (!colorWriteDisabled && colorPOI.readsDst()) ||
coveragePOI.readsDst()

?

[egdaniel, 2014-12-18 20:35:20]

The CQ bit was checked by egdaniel@google.com

[commit-bot: I haz the power, 2014-12-18 20:36:09]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/814933002/1

[commit-bot: I haz the power, 2014-12-18 20:45:00]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/9e4ecdc9f86724dcce23dc7546e2f295b901407b