Enable dual source blending for Vulkan

src/gpu/vk/GrVkPipelineStateBuilder.h

 /*
 * Copyright 2016 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
 
 #ifndef GrVkPipelineStateBuilder_DEFINED
 #define GrVkPipelineStateBuilder_DEFINED
 
@@ skipping 25 matching lines @@
                                                   GrPrimitiveType,
                                                   const GrVkPipelineState::Desc&,
                                                   const GrVkRenderPass& renderPass);
 
     const GrCaps* caps() const override;
     const GrGLSLCaps* glslCaps() const override;
 
     GrVkGpu* gpu() const { return fGpu; }
 
     void finalizeFragmentOutputColor(GrGLSLShaderVar& outputColor) override;
+    void finalizeFragmentSecondaryColor(GrGLSLShaderVar& outputColor) override;
 
 private:
     GrVkPipelineStateBuilder(GrVkGpu*,
                              const GrPipeline&,
                              const GrPrimitiveProcessor&,
                              const GrVkProgramDesc&);
 
     GrVkPipelineState* finalize(GrPrimitiveType primitiveType,
                                 const GrVkRenderPass& renderPass,
                                 const GrVkPipelineState::Desc&);
 
     static bool CreateVkShaderModule(const GrVkGpu* gpu,
                                      VkShaderStageFlagBits stage,
                                      const GrGLSLShaderBuilder& builder,
                                      VkShaderModule* shaderModule,
                                      VkPipelineShaderStageCreateInfo* stageInfo);
 
     GrGLSLUniformHandler* uniformHandler() override { return &fUniformHandler; }
     const GrGLSLUniformHandler* uniformHandler() const override { return &fUniformHandler; }
     GrGLSLVaryingHandler* varyingHandler() override { return &fVaryingHandler; }
 
     GrVkGpu* fGpu;
     GrVkVaryingHandler        fVaryingHandler;
     GrVkUniformHandler        fUniformHandler;
 
     typedef GrGLSLProgramBuilder INHERITED;
 };
 
 #endif