Update from https://crrev.com/319330
- New chromium clang rules require explicit external destructors so
  system/lib added for MessagePipe, DataPipe and SharedBuffer
- New chromium clang rules require override and no virtual in
  declarations, so many files updated.
- cc_strip_video patch updated.

BUG=
R=jamesr@chromium.org

Review URL: https://codereview.chromium.org/988693005
diff --git a/third_party/libxml/BUILD.gn b/third_party/libxml/BUILD.gn
index 992e92a..299a110 100644
--- a/third_party/libxml/BUILD.gn
+++ b/third_party/libxml/BUILD.gn
@@ -27,24 +27,43 @@
 static_library("libxml") {
   output_name = "libxml2"
   sources = [
-    "chromium/libxml_utils.h",
     "chromium/libxml_utils.cc",
+    "chromium/libxml_utils.h",
     "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/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",
+    "src/hash.c",
+    "src/include/libxml/DOCBparser.h",
+    "src/include/libxml/HTMLparser.h",
+    "src/include/libxml/HTMLtree.h",
+    "src/include/libxml/SAX.h",
+    "src/include/libxml/SAX2.h",
     "src/include/libxml/c14n.h",
     "src/include/libxml/catalog.h",
     "src/include/libxml/chvalid.h",
     "src/include/libxml/debugXML.h",
     "src/include/libxml/dict.h",
-    "src/include/libxml/DOCBparser.h",
     "src/include/libxml/encoding.h",
     "src/include/libxml/entities.h",
     "src/include/libxml/globals.h",
     "src/include/libxml/hash.h",
-    "src/include/libxml/HTMLparser.h",
-    "src/include/libxml/HTMLtree.h",
     "src/include/libxml/list.h",
     "src/include/libxml/nanoftp.h",
     "src/include/libxml/nanohttp.h",
@@ -52,8 +71,6 @@
     "src/include/libxml/parserInternals.h",
     "src/include/libxml/pattern.h",
     "src/include/libxml/relaxng.h",
-    "src/include/libxml/SAX.h",
-    "src/include/libxml/SAX2.h",
     "src/include/libxml/schemasInternals.h",
     "src/include/libxml/schematron.h",
     "src/include/libxml/threads.h",
@@ -62,10 +79,10 @@
     "src/include/libxml/valid.h",
     "src/include/libxml/xinclude.h",
     "src/include/libxml/xlink.h",
+    "src/include/libxml/xmlIO.h",
     "src/include/libxml/xmlautomata.h",
     "src/include/libxml/xmlerror.h",
     "src/include/libxml/xmlexports.h",
-    "src/include/libxml/xmlIO.h",
     "src/include/libxml/xmlmemory.h",
     "src/include/libxml/xmlmodule.h",
     "src/include/libxml/xmlreader.h",
@@ -81,21 +98,6 @@
     "src/include/libxml/xpointer.h",
     "src/include/win32config.h",
     "src/include/wsockcompat.h",
-    "src/acconfig.h",
-    "src/c14n.c",
-    "src/catalog.c",
-    "src/chvalid.c",
-    "src/debugXML.c",
-    "src/dict.c",
-    "src/DOCBparser.c",
-    "src/elfgcchack.h",
-    "src/encoding.c",
-    "src/entities.c",
-    "src/error.c",
-    "src/globals.c",
-    "src/hash.c",
-    "src/HTMLparser.c",
-    "src/HTMLtree.c",
     "src/legacy.c",
     "src/libxml.h",
     "src/list.c",
@@ -105,8 +107,6 @@
     "src/parserInternals.c",
     "src/pattern.c",
     "src/relaxng.c",
-    "src/SAX.c",
-    "src/SAX2.c",
     "src/schematron.c",
     "src/threads.c",
     "src/tree.c",