Update expat to 2.2.0 to fix CVE vulnerability.

third_party/expat/README.chromium

 Name: Expat XML Parser
 Short Name: expat
 URL: http://sourceforge.net/projects/expat/
-Version: 2.1.0
+Version: 2.2.0
 License: MIT
 License File: files/COPYING
 Security Critical: yes
 
 Description:
   This is Expat XML parser - very lightweight C library for parsing XML.
   Expat is distributed under an MIT license detailed in files/COPYING.
 
   We include it here because libjingle depends on it.
 
 Local Modifications:
   Removed files that Chromium didn't need:
     lib/expat*.dsp
     lib/Makefile.MPW
     amiga/*
     bcb5/*
     conftools/*
     doc/*
     examples/*
+    m4/*
     tests/*
     vms/*
     win32/*
     xmlwf/*
+    aclocal.m4
+    CMake.README
+    CMakeLists.txt
     configure
-    configure.in
+    configure.ac
+    configureChecks.cmake
     Makefile.in
     expat.dsw
-    expat.dsw
+    expat.pc.in
+    expat_config.h.cmake
     expat_config.h.in
+    Makefile.in
   Edited:
     lib/winconfig.h (see winconfig.h.original for unmodified version)
-      * Added check on line 1751 of xmltok_impl.c to patch a
-        bug with the handling of utf-8 characters that leads to a crash.
-    lib/xmltok_impl.c (see xmltok_imp.c.original for unmodified version)
-      * Prevent a compiler warning when compiling with
-        WIN32_LEAN_AND_MEAN predefined.
     lib/xmlparse.c (see xmlparse.c.original for unmodified version)
-      * Apply https://hg.mozilla.org/releases/mozilla-esr31/rev/2f3e78643f5c
-        to prevent an integer overflow.
+      * Added line 713 of xmlparse.c to suppress compiling error.
+      * Apply expat patch, Fix double free error.
+        https://github.com/libexpat/libexpat/commit/7ae9c3d3af433cd4defe95234eae7dc8ed15637f
+      * Apply expat patch. expat 2.2.0 fixed CVE-2016-0718 but cause
+        other regression. expat's issue number is #539.
+        https://github.com/libexpat/libexpat/commit/af507cef2c93cb8d40062a0abe43a4f4e9158fb2
+        https://sourceforge.net/p/expat/bugs/539/
+    lib/xmltok.c (see xmltok.c.original for unmodified version)
+        Also expat issue #539.
+        https://github.com/libexpat/libexpat/commit/896b6c1fd3b842f377d1b62135dccf0a579cf65d
+    lib/expat_external.h(see expat_external.h for unmodified version)
+      * Disallow adding symbol visibility attribute automatically to
+        function for static linked library.
   Added files:
     lib/expat_config.h (a generated config file)
+
+  Old CVE-2015-1283 fix for expat 2.1.0 from mozilla hg
+    https://hg.mozilla.org/releases/mozilla-esr31/rev/2f3e78643f5c
+    is included in expat 2.2.0.
+    https://github.com/libexpat/libexpat/commit/ba0f9c3b40c264b8dd392e02a7a060a8fa54f032