add/fix copyrights

src/opts/SkXfermode_opts_none.cpp

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
 #include "SkXfermode.h"
 #include "SkXfermode_proccoeff.h"
 
 // The prototypes below are for Clang
 extern SkProcCoeffXfermode* SkPlatformXfermodeFactory(const ProcCoeff& rec,
                                                       SkXfermode::Mode mode);
 
 extern SkXfermodeProc SkPlatformXfermodeProcFactory(SkXfermode::Mode mode);
 
 SkProcCoeffXfermode* SkPlatformXfermodeFactory(const ProcCoeff& rec,
                                                SkXfermode::Mode mode) {
     return NULL;
 }
 
 SkXfermodeProc SkPlatformXfermodeProcFactory(SkXfermode::Mode mode) {
     return NULL;
 }