[4fGradient] Veto blitters for non-opaque paints

src/effects/gradients/Sk4fLinearGradient.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "Sk4fLinearGradient.h"
 #include "Sk4x4f.h"
 #include "SkXfermode.h"
@@ skipping 401 matching lines @@
     }
 }
 
 bool SkLinearGradient::LinearGradient4fContext::onChooseBlitProcs(const SkImageInfo& info,
                                                                   BlitState* state) {
     SkXfermode::Mode mode;
     if (!SkXfermode::AsMode(state->fXfer, &mode)) {
         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;
     }
 
     switch (info.colorType()) {
         case kN32_SkColorType:
             state->fBlitBW = D32_BlitBW;
             return true;
         case kRGBA_F16_SkColorType:
             state->fBlitBW = D64_BlitBW;
             return true;
@@ skipping 36 matching lines @@
         static_cast<const LinearGradient4fContext*>(state->fCtx);
 
     if (ctx->fColorsArePremul) {
         ctx->shadePremulSpan<DstType::F16, ApplyPremul::False>(
             x, y, dst.writable_addr64(x, y), count);
     } else {
         ctx->shadePremulSpan<DstType::F16, ApplyPremul::True>(
             x, y, dst.writable_addr64(x, y), count);
     }
 }