XFA: Rename libpng to libpng16.

third_party/BUILD.gn

Index: third_party/BUILD.gn
diff --git a/third_party/BUILD.gn b/third_party/BUILD.gn
index d8d1dd227072d7b140590a48de8871f287953f23..2468dd4e5de8384db685a92d5f7fe8901c322ac8 100644
--- a/third_party/BUILD.gn
+++ b/third_party/BUILD.gn
@@ -278,28 +278,28 @@ source_set("fx_lpng") {
     "//third_party/pdfium:pdfium_config",
   ]
   sources = [
-    "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",
+    "libpng16/png.c",
+    "libpng16/png.h",
+    "libpng16/pngconf.h",
+    "libpng16/pngdebug.h",
+    "libpng16/pngerror.c",
+    "libpng16/pngget.c",
+    "libpng16/pnginfo.h",
+    "libpng16/pnglibconf.h",
+    "libpng16/pngmem.c",
+    "libpng16/pngpread.c",
+    "libpng16/pngpriv.h",
+    "libpng16/pngread.c",
+    "libpng16/pngrio.c",
+    "libpng16/pngrtran.c",
+    "libpng16/pngrutil.c",
+    "libpng16/pngset.c",
+    "libpng16/pngstruct.h",
+    "libpng16/pngtrans.c",
+    "libpng16/pngwio.c",
+    "libpng16/pngwrite.c",
+    "libpng16/pngwtran.c",
+    "libpng16/pngwutil.c",
   ]
 }