Add some backend flexibility for shader declarations in ProgramBuilding.

src/gpu/glsl/GrGLSLVarying.cpp

Index: src/gpu/glsl/GrGLSLVarying.cpp
diff --git a/src/gpu/glsl/GrGLSLVarying.cpp b/src/gpu/glsl/GrGLSLVarying.cpp
index 279dd5937e92a911b67891012a93cde96895b4f3..ea52fbe7ab9cf1972b7ae82921c22ea9a8ce28de 100644
--- a/src/gpu/glsl/GrGLSLVarying.cpp
+++ b/src/gpu/glsl/GrGLSLVarying.cpp
@@ -105,6 +105,10 @@ void GrGLSLVaryingHandler::addAttribute(const GrShaderVar& var) {
     fVertexInputs.push_back(var);
 }
 
+void GrGLSLVaryingHandler::finalize() {
+    this->onFinalize();
+}
+
 void GrGLSLVaryingHandler::appendDecls(const VarArray& vars, SkString* out) const {
     for (int i = 0; i < vars.count(); ++i) {
         vars[i].appendDecl(fProgramBuilder->glslCaps(), out);