Add in shader blending for CoverageSetOp XP

src/gpu/glsl/GrGLSLXferProcessor.h

Index: src/gpu/glsl/GrGLSLXferProcessor.h
diff --git a/src/gpu/glsl/GrGLSLXferProcessor.h b/src/gpu/glsl/GrGLSLXferProcessor.h
index 46d775d405176c8785eee8d25ac09d569e2213d9..3707d934592b3a4f0141001b80e9b68bffb60d79 100644
--- a/src/gpu/glsl/GrGLSLXferProcessor.h
+++ b/src/gpu/glsl/GrGLSLXferProcessor.h
@@ -85,8 +85,10 @@ private:
     virtual void emitBlendCodeForDstRead(GrGLSLXPBuilder*,
                                          GrGLSLXPFragmentBuilder*,
                                          const char* srcColor,
+                                         const char* srcCoverage,
                                          const char* dstColor,
                                          const char* outColor,
+                                         const char* outColorSecondary,
                                          const GrXferProcessor&) {
         SkFAIL("emitBlendCodeForDstRead not implemented.");
     }