XFA: Upgrade libpng to 1.6.20.

third_party/third_party.gyp

Index: third_party/third_party.gyp
diff --git a/third_party/third_party.gyp b/third_party/third_party.gyp
index 54b6aa31a279bbb0990ab943a410ae859421d1fd..f653760c49725eb7dda49bcb76ff2418e5d6fb6d 100644
--- a/third_party/third_party.gyp
+++ b/third_party/third_party.gyp
@@ -269,22 +269,28 @@
       'target_name': 'fx_lpng',
       'type': 'static_library',
       'sources': [
-        'lpng_v163/png.h',
-        'lpng_v163/png.c',
-        'lpng_v163/pngerror.c',
-        'lpng_v163/pngget.c',
-        'lpng_v163/pngmem.c',
-        'lpng_v163/pngpread.c',
-        'lpng_v163/pngread.c',
-        'lpng_v163/pngrio.c',
-        'lpng_v163/pngrtran.c',
-        'lpng_v163/pngrutil.c',
-        'lpng_v163/pngset.c',
-        'lpng_v163/pngtrans.c',
-        'lpng_v163/pngwio.c',
-        'lpng_v163/pngwrite.c',
-        'lpng_v163/pngwtran.c',
-        'lpng_v163/pngwutil.c',
+        'libpng/png.c',
+        'libpng/png.h',
+        'libpng/pngconf.h',
+        'libpng/pngdebug.h',
+        'libpng/pngerror.c',
+        'libpng/pngget.c',
+        'libpng/pnginfo.h',
+        'libpng/pnglibconf.h',
+        'libpng/pngmem.c',
+        'libpng/pngpread.c',
+        'libpng/pngpriv.h',
+        'libpng/pngread.c',
+        'libpng/pngrio.c',
+        'libpng/pngrtran.c',
+        'libpng/pngrutil.c',
+        'libpng/pngset.c',
+        'libpng/pngstruct.h',
+        'libpng/pngtrans.c',
+        'libpng/pngwio.c',
+        'libpng/pngwrite.c',
+        'libpng/pngwtran.c',
+        'libpng/pngwutil.c',
       ],
     },
     {