Turn disallowed URL patterns such as <all_urls> for externally_connectable into

extensions/common/install_warning.h

 // Copyright (c) 2013 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.
 
 #ifndef EXTENSIONS_COMMON_INSTALL_WARNING_H_
 #define EXTENSIONS_COMMON_INSTALL_WARNING_H_
 
 #include <ostream>
 #include <string>
 
 namespace extensions {
 
 struct InstallWarning {
   enum Format {
     // IMPORTANT: Do not build HTML strings from user or developer-supplied
     // input.
     FORMAT_TEXT,
     FORMAT_HTML,
   };
+  static InstallWarning Text(const std::string& message) {
+    return InstallWarning(FORMAT_TEXT, message);
+  }
   InstallWarning(Format format, const std::string& message)
       : format(format), message(message) {
   }
   bool operator==(const InstallWarning& other) const {
     return format == other.format && message == other.message;
   }
   Format format;
   std::string message;
 };
 
 // Let gtest print InstallWarnings.
 void PrintTo(const InstallWarning&, ::std::ostream* os);
 
 }  // namespace
 
 #endif  // EXTENSIONS_COMMON_INSTALL_WARNING_H_