Use shader based blending to clamp kPlus mode w/F16

Bug: skia:6173
Change-Id: I21042d484d9a7b3eee04aa3301d9793d00ad6908
Reviewed-on: https://skia-review.googlesource.com/48183
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
diff --git a/src/gpu/ops/GrRegionOp.cpp b/src/gpu/ops/GrRegionOp.cpp
index 23a5020..177a185 100644
--- a/src/gpu/ops/GrRegionOp.cpp
+++ b/src/gpu/ops/GrRegionOp.cpp
@@ -98,9 +98,10 @@
 
     FixedFunctionFlags fixedFunctionFlags() const override { return fHelper.fixedFunctionFlags(); }
 
-    RequiresDstTexture finalize(const GrCaps& caps, const GrAppliedClip* clip) override {
-        return fHelper.xpRequiresDstTexture(caps, clip, GrProcessorAnalysisCoverage::kNone,
-                                            &fRegions[0].fColor);
+    RequiresDstTexture finalize(const GrCaps& caps, const GrAppliedClip* clip,
+                                GrPixelConfigIsClamped dstIsClamped) override {
+        return fHelper.xpRequiresDstTexture(caps, clip, dstIsClamped,
+                                            GrProcessorAnalysisCoverage::kNone, &fRegions[0].fColor);
     }
 
 private: