Moved/renamed EscapeString from visual_studio_writer to XmlEscape in xml_element_writer.

tools/gn/xml_element_writer.cc

Index: tools/gn/xml_element_writer.cc
diff --git a/tools/gn/xml_element_writer.cc b/tools/gn/xml_element_writer.cc
index fcf34b283cce6ad473f29f6a745be78ff4062e38..bb0d23262157fc58e744cfc981a8ebf264d862f6 100644
--- a/tools/gn/xml_element_writer.cc
+++ b/tools/gn/xml_element_writer.cc
@@ -81,3 +81,35 @@ std::ostream& XmlElementWriter::StartContent(bool start_new_line) {
 
   return out_;
 }
+
+std::string XmlEscape(const std::string& value) {
+  std::string result;
+  for (char c : value) {
+    switch (c) {
+      case '\n':
+        result += "
";
+        break;
+      case '\r':
+        result += "
";
+        break;
+      case '\t':
+        result += "	";
+        break;
+      case '"':
+        result += """;
+        break;
+      case '<':
+        result += "&lt;";
+        break;
+      case '>':
+        result += "&gt;";
+        break;
+      case '&':
+        result += "&amp;";
+        break;
+      default:
+        result += c;
+    }
+  }
+  return result;
+}