Moved/renamed EscapeString from visual_studio_writer to XmlEscape in xml_element_writer.

tools/gn/xml_element_writer.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "tools/gn/xml_element_writer.h"
 
 #include "base/memory/ptr_util.h"
 
 XmlAttributes::XmlAttributes() {}
 
@@ skipping 63 matching lines @@
     opening_tag_finished_ = true;
 
     if (start_new_line && one_line_) {
       out_ << std::endl;
       one_line_ = false;
     }
   }
 
   return out_;
 }
+
+std::string XmlEscape(const std::string& value) {
+  std::string result;
+  for (char c : value) {
+    switch (c) {
+      case '\n':
+        result += "&#10;";
+        break;
+      case '\r':
+        result += "&#13;";
+        break;
+      case '\t':
+        result += "&#9;";
+        break;
+      case '"':
+        result += "&quot;";
+        break;
+      case '<':
+        result += "&lt;";
+        break;
+      case '>':
+        result += "&gt;";
+        break;
+      case '&':
+        result += "&amp;";
+        break;
+      default:
+        result += c;
+    }
+  }
+  return result;
+}