Added function CreateFrom2Procs() in new namespace GrXfermodeFragmentProcessor

include/gpu/effects/GrXfermodeFragmentProcessor.h

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrXfermodeFragmentProcessor_DEFINED
+#define GrXfermodeFragmentProcessor_DEFINED
+
+#include "SkXfermode.h"
+
+class GrFragmentProcessor;
+
+namespace GrXfermodeFragmentProcessor {
+    const GrFragmentProcessor* CreateFromTwoProcessors(const GrFragmentProcessor* src,
+                                                       const GrFragmentProcessor* dst,
+                                                       SkXfermode::Mode mode);
+};
+
+#endif