starter procs for blending with pm4f

src/core/SkXfer4f.h

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkXfermodePriv_DEFINED
+#define SkXfermodePriv_DEFINED
+
+#include "SkXfermode.h"
+
+enum SkXfef4fFlags {
+    kSrcIsOpaque_SkXfer4fFlag   = 1 << 0,
+    kDstIsSRGB_SkXfer4fFlag     = 1 << 1,
+};
+
+typedef void (*SkPM4fXfer1Proc)(uint32_t dst[], const SkPM4f& src, int count);
+typedef void (*SkPM4fXferNProc)(uint32_t dst[], const SkPM4f src[], int count);
+
+SkPM4fXfer1Proc SkPM4fXfer1ProcFactory(SkXfermode::Mode, uint32_t flags);
+SkPM4fXferNProc SkPM4fXferNProcFactory(SkXfermode::Mode, uint32_t flags);
+
+#endif