Enable dual source blending for Vulkan

src/gpu/vk/GrVkPipelineStateBuilder.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 "vk/GrVkPipelineStateBuilder.h"
 
 #include "vk/GrVkGpu.h"
@@ skipping 35 matching lines @@
     return fGpu->caps();
 }
 const GrGLSLCaps* GrVkPipelineStateBuilder::glslCaps() const {
     return fGpu->vkCaps().glslCaps();
 }
 
 void GrVkPipelineStateBuilder::finalizeFragmentOutputColor(GrGLSLShaderVar& outputColor) {
     outputColor.setLayoutQualifier("location = 0");
 }
 
+void GrVkPipelineStateBuilder::finalizeFragmentSecondaryColor(GrGLSLShaderVar& outputColor) {
+    outputColor.setLayoutQualifier("location = 1");
+}
+
 VkShaderStageFlags visibility_to_vk_stage_flags(uint32_t visibility) {
     VkShaderStageFlags flags = 0;
 
     if (visibility & kVertex_GrShaderFlag) {
         flags |= VK_SHADER_STAGE_VERTEX_BIT;
     }
     if (visibility & kGeometry_GrShaderFlag) {
         flags |= VK_SHADER_STAGE_GEOMETRY_BIT;
     }
     if (visibility & kFragment_GrShaderFlag) {
@@ skipping 225 matching lines @@
                                  dsLayout,
                                  fUniformHandles,
                                  fUniformHandler.fUniforms,
                                  fUniformHandler.fCurrentVertexUBOOffset,
                                  fUniformHandler.fCurrentFragmentUBOOffset,
                                  numSamplers,
                                  fGeometryProcessor,
                                  fXferProcessor,
                                  fFragmentProcessors);
 }