Upgrade to libxml 2.9.2 and libxslt 1.1.28

third_party/libxml/BUILD.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Define an "os_include" variable that points at the OS-specific generated
 # headers.  These were generated by running the configure script offline.
 if (is_linux || is_android || is_nacl) {
   os_include = "linux"
 } else if (is_mac || is_ios) {
   os_include = "mac"
@@ skipping 21 matching lines @@
     "linux/config.h",
     "linux/include/libxml/xmlversion.h",
     "mac/config.h",
     "mac/include/libxml/xmlversion.h",
     "src/DOCBparser.c",
     "src/HTMLparser.c",
     "src/HTMLtree.c",
     "src/SAX.c",
     "src/SAX2.c",
     "src/acconfig.h",
+    "src/buf.c",
+    "src/buf.h",
     "src/c14n.c",
     "src/catalog.c",
     "src/chvalid.c",
     "src/debugXML.c",
     "src/dict.c",
     "src/elfgcchack.h",
     "src/encoding.c",
     "src/entities.c",
     "src/error.c",
     "src/globals.c",
@@ skipping 119 matching lines @@
       "-Wno-tautological-pointer-compare",
 
       # threads.c attempts to forward declare a pthread_equal which doesn't
       # match the prototype in pthreads.h
       "-Wno-ignored-attributes",
     ]
   }
 
   include_dirs = [ "$os_include" ]
 }