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/PrimitiveProcessorTest.cpp b/tests/PrimitiveProcessorTest.cpp
index 47dff33..6402020 100644
--- a/tests/PrimitiveProcessorTest.cpp
+++ b/tests/PrimitiveProcessorTest.cpp
@@ -38,7 +38,8 @@
         return FixedFunctionFlags::kNone;
     }
 
-    RequiresDstTexture finalize(const GrCaps& caps, const GrAppliedClip* clip) override {
+    RequiresDstTexture finalize(const GrCaps&, const GrAppliedClip*,\
+                                GrPixelConfigIsClamped) override {
         return RequiresDstTexture::kNo;
     }