SkPDF: Implement Paeth predictor for images.

src/pdf/SkPngPredictors.h

Index: src/pdf/SkPngPredictors.h
diff --git a/src/pdf/SkPngPredictors.h b/src/pdf/SkPngPredictors.h
new file mode 100644
index 0000000000000000000000000000000000000000..47db6d8d0c06ae386a59fac2aef130617f46daa5
--- /dev/null
+++ b/src/pdf/SkPngPredictors.h
@@ -0,0 +1,15 @@
+/*
+ * 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 SkPngPredictors_DEFINED
+#define SkPngPredictors_DEFINED
+
+#include "stdint.h"

[mtklein, 2016/02/19 21:53:07]

<stdint.h>, or "SkTypes.h"

+
+void SkPaethEncode3(int width, const uint8_t* prev, const uint8_t* scanline, uint8_t* out);

[mtklein, 2016/02/19 21:53:07]

Note whether width is in bytes or pixels?

+void SkPaethEncode1(int width, const uint8_t* prev, const uint8_t* scanline, uint8_t* out);
+
+#endif  // SkPngPredictors_DEFINED