Add ability to extract YUV planes from SkImage

src/gpu/GrTextureToYUVPlanes.h

Index: src/gpu/GrTextureToYUVPlanes.h
diff --git a/src/gpu/GrTextureToYUVPlanes.h b/src/gpu/GrTextureToYUVPlanes.h
new file mode 100644
index 0000000000000000000000000000000000000000..67b6fce2eb1fceb25b40d8636b7e3c7d75e98e2f
--- /dev/null
+++ b/src/gpu/GrTextureToYUVPlanes.h
@@ -0,0 +1,19 @@
+/*
+ * 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 GrTextureToYUVPlanes_DEFINED
+#define GrTextureToYUVPlanes_DEFINED
+
+#include "SkImageInfo.h"
+#include "SkSize.h"
+
+class GrTexture;
+
+bool GrTextureToYUVPlanes(GrTexture* texture, const SkISize[3], void* const planes[3],
+                          const size_t rowBytes[3], SkYUVColorSpace);
+
+#endif