Implement support for KHR_blend_equation_advanced

src/gpu/gl/GrGLGpu.h

Index: src/gpu/gl/GrGLGpu.h
diff --git a/src/gpu/gl/GrGLGpu.h b/src/gpu/gl/GrGLGpu.h
index 29d63fbd4feae7536cc6af633f2ce9bb0e658a9a..6e82a8c15cec3047d66974d480d010694e082365 100644
--- a/src/gpu/gl/GrGLGpu.h
+++ b/src/gpu/gl/GrGLGpu.h
@@ -105,6 +105,8 @@ public:
                         const SkIRect& srcRect,
                         const SkIPoint& dstPoint) override;
 
+    void setXferBarrier(GrXferBarrierType) override;
+
     void buildProgramDesc(GrProgramDesc*,
                           const GrPrimitiveProcessor&,
                           const GrPipeline&,
@@ -434,6 +436,7 @@ private:
     } fHWGeometryState;
 
     struct {
+        GrBlendEquation fEquation;
         GrBlendCoeff    fSrcCoeff;
         GrBlendCoeff    fDstCoeff;
         GrColor         fConstColor;
@@ -441,6 +444,7 @@ private:
         TriState        fEnabled;
 
         void invalidate() {
+            fEquation = kInvalid_GrBlendEquation;
             fSrcCoeff = kInvalid_GrBlendCoeff;
             fDstCoeff = kInvalid_GrBlendCoeff;
             fConstColorValid = false;