[4fGradient] Veto blitters for non-opaque paints

src/effects/gradients/Sk4fLinearGradient.cpp

Index: src/effects/gradients/Sk4fLinearGradient.cpp
diff --git a/src/effects/gradients/Sk4fLinearGradient.cpp b/src/effects/gradients/Sk4fLinearGradient.cpp
index 4ea025d0d2781b995ee03e42fcc80bfdcd0d83ad..090bdaa83555ab5dd6a4cf3b279416c075393da1 100644
--- a/src/effects/gradients/Sk4fLinearGradient.cpp
+++ b/src/effects/gradients/Sk4fLinearGradient.cpp
@@ -419,9 +419,8 @@ bool SkLinearGradient::LinearGradient4fContext::onChooseBlitProcs(const SkImageI
         return false;
     }
 
-    const SkGradientShaderBase& shader = static_cast<const SkGradientShaderBase&>(fShader);
     if (mode != SkXfermode::kSrc_Mode &&
-        !(mode == SkXfermode::kSrcOver_Mode && shader.colorsAreOpaque())) {
+        !(mode == SkXfermode::kSrcOver_Mode && (fFlags & kOpaqueAlpha_Flag))) {
         return false;
     }