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/GrTextureOp.cpp b/src/gpu/ops/GrTextureOp.cpp
index 732b9c9..5dc30f3 100644
--- a/src/gpu/ops/GrTextureOp.cpp
+++ b/src/gpu/ops/GrTextureOp.cpp
@@ -276,7 +276,8 @@
         return str;
     }
 
-    RequiresDstTexture finalize(const GrCaps& caps, const GrAppliedClip* clip) override {
+    RequiresDstTexture finalize(const GrCaps& caps, const GrAppliedClip* clip,
+                                GrPixelConfigIsClamped dstIsClamped) override {
         SkASSERT(!fFinalized);
         SkASSERT(1 == fProxyCnt);
         fFinalized = true;