SkLS accepts nullptr for pointer args, handles alpha accurately, has new GM

include/gpu/GrFragmentProcessor.h

Index: include/gpu/GrFragmentProcessor.h
diff --git a/include/gpu/GrFragmentProcessor.h b/include/gpu/GrFragmentProcessor.h
index b8ebeca30320b3f8a8e21e33e4a16395ef8d5bf2..bda132eec97e3b7241d0f815412fc15ff85c1142 100644
--- a/include/gpu/GrFragmentProcessor.h
+++ b/include/gpu/GrFragmentProcessor.h
@@ -48,6 +48,12 @@ public:
     static sk_sp<GrFragmentProcessor> OverrideInput(sk_sp<GrFragmentProcessor>, GrColor);
 
     /**
+     *  Returns a fragment processor that runs 2 children in series, first a FP that premuls the

[egdaniel, 2016/07/14 03:22:47]

I think just saying something like "Returns a fragment processor that premuls
the input before calling the passed in fragment processor" is sufficient. There
is no need to get into the details of children or running in series.

[dvonbeck, 2016/07/14 14:30:33]

Done.

+     *  input color and sets it as its output, and then the passed FP.
+     */
+    static sk_sp<GrFragmentProcessor> PremulInput(sk_sp<GrFragmentProcessor>);
+
+    /**
      * Returns a fragment processor that runs the passed in array of fragment processors in a
      * series. The original input is passed to the first, the first's output is passed to the
      * second, etc. The output of the returned processor is the output of the last processor of the