Upgrade to libxml 2.9.2 and libxslt 1.1.28

third_party/libxslt/BUILD.gn

Index: third_party/libxslt/BUILD.gn
diff --git a/third_party/libxslt/BUILD.gn b/third_party/libxslt/BUILD.gn
index 13800851888877160c097bddbc4ac46de2e83ffe..7a9979bb0cb75d89867de79e21f6430436782de1 100644
--- a/third_party/libxslt/BUILD.gn
+++ b/third_party/libxslt/BUILD.gn
@@ -56,6 +56,7 @@ static_library("libxslt") {
     "libxslt/xsltwin32config.h",
     "linux/config.h",
     "mac/config.h",
+    "win32/config.h",
   ]
 
   configs -= [ "//build/config/compiler:chromium_code" ]
@@ -66,6 +67,7 @@ static_library("libxslt") {
     include_dirs = [ "linux" ]
   } else if (is_win) {
     include_dirs = [ "win32" ]
+    cflags = [ "/wd4267" ]  # size_t to int.
   } else if (is_mac) {
     include_dirs = [ "mac" ]
   }