Remove hasMixedSamples() from GrPipelineBuilder

src/effects/SkArithmeticMode_gpu.h

Index: src/effects/SkArithmeticMode_gpu.h
diff --git a/src/effects/SkArithmeticMode_gpu.h b/src/effects/SkArithmeticMode_gpu.h
index a44ac11e745440ff47796c519e36e92aa213c4d9..b8a40cf827216de27fcf8755b31e97d3fa60b4e3 100644
--- a/src/effects/SkArithmeticMode_gpu.h
+++ b/src/effects/SkArithmeticMode_gpu.h
@@ -92,9 +92,7 @@ private:
                                            bool hasMixedSamples,
                                            const DstTexture*) const override;
 
-    bool onWillReadDstColor(const GrCaps& caps,
-                            const GrPipelineOptimizations& optimizations,
-                            bool hasMixedSamples) const override {
+    bool onWillReadDstColor(const GrCaps&, const GrPipelineOptimizations&) const override {
         return true;
     }