stop using SkXfermode -- use SkBlendMode instead

Massive (mostly mechanical) refactoring from one enum name to another.

This allows us to undefine SK_SUPPORT_LEGACY_XFERMODE_IS_PUBLIC, so we can (next) eliminate SkXfermode.h entirely

BUG=652484
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel
TBR=

Review-Url: https://codereview.chromium.org/2502373003
Cr-Commit-Position: refs/heads/master@{#433788}
85 files changed