Fix building with unbundled libxml

Add new targets to libxml.gn that were added in
 https://chromium-review.googlesource.com/c/chromium/src/+/1894877
Adjust includes to use system libxml headers too

Bug: 1043042
Change-Id: I948c063e212e49b9e7f42fed2b8bf7f4af042ca7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2007110Reviewed-by: Robert Sesek <rsesek@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Robert Sesek <rsesek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#735957}

build/linux/unbundle/libxml.gn

@@ -8,11 +8,48 @@ pkg_config("system_libxml") {
   packages = [ "libxml-2.0" ]
 }
 
-static_library("libxml") {
+source_set("libxml") {
+  public_configs = [ ":system_libxml" ]
+}
+
+static_library("libxml_utils") {
+  # Do not expand this visibility list without first consulting with the
+  # Security Team.
+  visibility = [
+    ":xml_reader",
+    ":xml_writer",
+    "//base/test:test_support",
+    "//services/data_decoder:xml_parser_fuzzer",
+  ]
   sources = [
     "chromium/libxml_utils.cc",
     "chromium/libxml_utils.h",
   ]
-
   public_configs = [ ":system_libxml" ]
 }
+
+static_library("xml_reader") {
+  # Do not expand this visibility list without first consulting with the
+  # Security Team.
+  visibility = [
+    "//base/test:test_support",
+    "//components/policy/core/common:unit_tests",
+    "//services/data_decoder:*",
+    "//tools/traffic_annotation/auditor:auditor_sources",
+  ]
+  sources = [
+    "chromium/xml_reader.cc",
+    "chromium/xml_reader.h",
+  ]
+  deps = [ ":libxml_utils" ]
+}
+
+static_library("xml_writer") {
+  # The XmlWriter is considered safe to use from any target.
+  visibility = [ "*" ]
+  sources = [
+    "chromium/xml_writer.cc",
+    "chromium/xml_writer.h",
+  ]
+  deps = [ ":libxml_utils" ]
+}

third_party/libxml/chromium/libxml_utils.h

@@ -5,9 +5,9 @@
 #ifndef THIRD_PARTY_LIBXML_CHROMIUM_LIBXML_UTILS_H_
 #define THIRD_PARTY_LIBXML_CHROMIUM_LIBXML_UTILS_H_
 
-#include <string>
+#include <libxml/xmlreader.h>
 
-#include "third_party/libxml/src/include/libxml/xmlreader.h"
+#include <string>
 
 // libxml uses a global error function pointer for reporting errors.
 // A ScopedXmlErrorFunc object lets you change the global error pointer

third_party/libxml/chromium/xml_reader.cc

@@ -4,10 +4,11 @@
 
 #include "third_party/libxml/chromium/xml_reader.h"
 
+#include <libxml/xmlreader.h>
+
 #include <vector>
 
 #include "third_party/libxml/chromium/libxml_utils.h"
-#include "third_party/libxml/src/include/libxml/xmlreader.h"
 
 using internal::XmlStringToStdString;
 

third_party/libxml/chromium/xml_writer.cc

@@ -4,8 +4,9 @@
 
 #include "third_party/libxml/chromium/xml_writer.h"
 
+#include <libxml/xmlwriter.h>
+
 #include "third_party/libxml/chromium/libxml_utils.h"
-#include "third_party/libxml/src/include/libxml/xmlwriter.h"
 
 XmlWriter::XmlWriter() : writer_(nullptr), buffer_(nullptr) {}