rebase

TBR=
NOTRY=True
BUG=skia:

Review URL: https://codereview.chromium.org/812423002
adding bleed back to ignore

TBR=
NOTRY=True
BUG=skia:

Review URL: https://codereview.chromium.org/810713003
I could create new GMs if you prefer.

BUG=skia:

Review URL: https://codereview.chromium.org/812163002
rebase
NOTRY=True
TBR=
BUG=skia:

Review URL: https://codereview.chromium.org/798323006
improve precision of gradients (disabled for now)

BUG=skia:2898
TBR=caryclark

Review URL: https://codereview.chromium.org/815623004
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:

Review URL: https://codereview.chromium.org/814933002
remove dead code behind SK_SUPPORT_LEGACY_ALLOCPIXELS_BOOL

BUG=skia:

Review URL: https://codereview.chromium.org/814753004