Implement support for KHR_blend_equation_advanced

src/gpu/gl/builders/GrGLShaderBuilder.cpp

Index: src/gpu/gl/builders/GrGLShaderBuilder.cpp
diff --git a/src/gpu/gl/builders/GrGLShaderBuilder.cpp b/src/gpu/gl/builders/GrGLShaderBuilder.cpp
index e885d36a4373708cf46c609a565af119737d265b..67fbe2451dc4c148977c2a1ce10df4675c384f78 100644
--- a/src/gpu/gl/builders/GrGLShaderBuilder.cpp
+++ b/src/gpu/gl/builders/GrGLShaderBuilder.cpp
@@ -173,7 +173,8 @@ void GrGLShaderBuilder::appendTextureLookup(const char* samplerName,
 }
 
 void GrGLShaderBuilder::addLayoutQualifier(const char* param, InterfaceQualifier interface) {
-    SkASSERT(fProgramBuilder->gpu()->glslGeneration() >= k330_GrGLSLGeneration);
+    SkASSERT(fProgramBuilder->gpu()->glslGeneration() >= k330_GrGLSLGeneration ||
+             fProgramBuilder->gpu()->glCaps().glslCaps()->mustEnableAdvBlendEqs());
     fLayoutParams[interface].push_back() = param;
 }