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

include/gpu/GrFragmentProcessor.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrFragmentProcessor_DEFINED
 #define GrFragmentProcessor_DEFINED
 
@@ skipping 30 matching lines @@
     static sk_sp<GrFragmentProcessor> MulOutputByInputUnpremulColor(sk_sp<GrFragmentProcessor>);
 
     /**
      *  Returns a parent fragment processor that adopts the passed fragment processor as a child.
      *  The parent will ignore its input color and instead feed the passed in color as input to the
      *  child.
      */
     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
      * series.
      *
      * The array elements with be moved.
      */
     static sk_sp<GrFragmentProcessor> RunInSeries(sk_sp<GrFragmentProcessor>*, int cnt);
 
     GrFragmentProcessor()
@@ skipping 161 matching lines @@
     /**
      * This is not SkSTArray<1, sk_sp<GrFragmentProcessor>> because this class holds strong
      * references until notifyRefCntIsZero and then it holds pending executions.
      */
     SkSTArray<1, GrFragmentProcessor*, true>    fChildProcessors;
 
     typedef GrProcessor INHERITED;
 };
 
 #endif