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/tests/GrMeshTest.cpp b/tests/GrMeshTest.cpp
index d174675..dac9deb 100644
--- a/tests/GrMeshTest.cpp
+++ b/tests/GrMeshTest.cpp
@@ -262,7 +262,8 @@
 private:
     const char* name() const override { return "GrMeshTestOp"; }
     FixedFunctionFlags fixedFunctionFlags() const override { return FixedFunctionFlags::kNone; }
-    RequiresDstTexture finalize(const GrCaps&, const GrAppliedClip*) override {
+    RequiresDstTexture finalize(const GrCaps&, const GrAppliedClip*,
+                                GrPixelConfigIsClamped) override {
         return RequiresDstTexture::kNo;
     }
     bool onCombineIfPossible(GrOp* other, const GrCaps& caps) override { return false; }