SkPDF: Implement Paeth predictor for images.

gyp/pdf.gypi

 # 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 this gypi to include all 'pdf' files
 # The parent gyp/gypi file must define
 #       'skia_src_path'     e.g. skia/trunk/src
 #       'skia_include_path' e.g. skia/trunk/include
 #
 # The skia build defines these in common_variables.gypi
@@ skipping 23 matching lines @@
         '<(skia_src_path)/pdf/SkPDFResourceDict.cpp',
         '<(skia_src_path)/pdf/SkPDFResourceDict.h',
         '<(skia_src_path)/pdf/SkPDFShader.cpp',
         '<(skia_src_path)/pdf/SkPDFShader.h',
         '<(skia_src_path)/pdf/SkPDFStream.cpp',
         '<(skia_src_path)/pdf/SkPDFStream.h',
         '<(skia_src_path)/pdf/SkPDFTypes.cpp',
         '<(skia_src_path)/pdf/SkPDFTypes.h',
         '<(skia_src_path)/pdf/SkPDFUtils.cpp',
         '<(skia_src_path)/pdf/SkPDFUtils.h',
+        '<(skia_src_path)/pdf/SkPngPredictors.cpp',
+        '<(skia_src_path)/pdf/SkPngPredictors.h',
     ],
 }