[GN] Adding missing source type for extension .appex.

tools/gn/xcode_object.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/xcode_object.h"
 
 #include <iomanip>
 #include <sstream>
 #include <utility>
 
@@ skipping 80 matching lines @@
 }
 
 struct SourceTypeForExt {
   const char* ext;
   const char* source_type;
 };
 
 const SourceTypeForExt kSourceTypeForExt[] = {
     {".a", "archive.ar"},
     {".app", "wrapper.application"},
+    {".appex", "wrapper.app-extension"},
     {".bdic", "file"},
     {".bundle", "wrapper.cfbundle"},
     {".c", "sourcecode.c.c"},
     {".cc", "sourcecode.cpp.cpp"},
     {".cpp", "sourcecode.cpp.cpp"},
     {".css", "text.css"},
     {".cxx", "sourcecode.cpp.cpp"},
     {".dart", "sourcecode"},
     {".dylib", "compiled.mach-o.dylib"},
     {".framework", "wrapper.framework"},
@@ skipping 747 matching lines @@
   const std::string indent_str(indent, '\t');
   const IndentRules rules = {false, indent + 1};
   out << indent_str << Reference() << " = {\n";
   PrintProperty(out, rules, "isa", ToString(Class()));
   PrintProperty(out, rules, "buildConfigurations", configurations_);
   PrintProperty(out, rules, "defaultConfigurationIsVisible", 1u);
   PrintProperty(out, rules, "defaultConfigurationName",
                 configurations_[0]->Name());
   out << indent_str << "};\n";
 }