Report optimizations in master gradient effects

All of the FPs for the gradient components have had to be updated to
include the @optimizationFlags section. Layout FPs now can use the
opacity preserving optimization to report whether or not they might
reject a fragment (e.g. 2 point conical gradients).

The previous composition logic that handled ensuring the gradient shader
output a premul color was removing optimizations that should have been
valid for gradients, so the make premul logic has been inlined into
the top-level effect FPs.

Bug: skia:
Change-Id: I73e4224d8dc0e3420a215b0aa805d829b08f6c76
Reviewed-on: https://skia-review.googlesource.com/151547
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
17 files changed