Remove GrBlendFragmentProcessor::Behavior::kSkBlendMode.

The only difference between this and kComposeOne is that it always
sets the src child's input color to opaque white. However, all call sites
pass a color FP that ignores its input. So in practice there is no
difference.

Bug: skia:10457
Change-Id: I816d421fcb7b48d81ba68f835571ef703aa8d73d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/425460
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/src/gpu/GrFragmentProcessor.h b/src/gpu/GrFragmentProcessor.h
index 84743c4..9fc1d31 100644
--- a/src/gpu/GrFragmentProcessor.h
+++ b/src/gpu/GrFragmentProcessor.h
@@ -61,14 +61,16 @@
 
     /**
      *  Returns a fragment processor that generates the passed-in color, modulated by the child's
-     *  alpha channel. (Pass a null FP to use the alpha from fInputColor instead of a child FP.)
+     *  alpha channel. The child's input color will be the parent's fInputColor. (Pass a null FP to
+     *  use the alpha from fInputColor instead of a child FP.)
      */
     static std::unique_ptr<GrFragmentProcessor> ModulateAlpha(
             std::unique_ptr<GrFragmentProcessor> child, const SkPMColor4f& color);
 
     /**
      *  Returns a fragment processor that generates the passed-in color, modulated by the child's
-     *  RGBA color. (Pass a null FP to use the color from fInputColor instead of a child FP.)
+     *  RGBA color. The child's input color will be the parent's fInputColor. (Pass a null FP to use
+     *  the color from fInputColor instead of a child FP.)
      */
     static std::unique_ptr<GrFragmentProcessor> ModulateRGBA(
             std::unique_ptr<GrFragmentProcessor> child, const SkPMColor4f& color);