Update GrPaint APIs to reflect lack of multiple color processors.

Change-Id: Ic7799b3c5f4294cba9ff72f8c11a2ad285ab189f
Bug: skia:10217
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/304738
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
diff --git a/gm/sample_matrix_variable.cpp b/gm/sample_matrix_variable.cpp
index 84a34ab..9f2ab18 100644
--- a/gm/sample_matrix_variable.cpp
+++ b/gm/sample_matrix_variable.cpp
@@ -73,7 +73,7 @@
         auto fp = std::unique_ptr<GrFragmentProcessor>(
                 new SampleMatrixVariableEffect(std::move(baseFP), ofsX, ofsY));
         GrPaint paint;
-        paint.addColorFragmentProcessor(std::move(fp));
+        paint.setColorFragmentProcessor(std::move(fp));
         rtCtx->drawRect(nullptr, std::move(paint), GrAA::kNo, SkMatrix::Translate(tx, ty),
                         SkRect::MakeIWH(256, 256));
     };