Add an whitelist for calling GN's exec_script.

tools/gn/build_settings.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 TOOLS_GN_BUILD_SETTINGS_H_
 #define TOOLS_GN_BUILD_SETTINGS_H_
 
 #include <map>
+#include <set>
 
 #include "base/basictypes.h"
 #include "base/callback.h"
 #include "base/files/file_path.h"
 #include "base/memory/scoped_ptr.h"
 #include "tools/gn/args.h"
 #include "tools/gn/scope.h"
 #include "tools/gn/source_dir.h"
 #include "tools/gn/source_file.h"
 
@@ skipping 59 matching lines @@
     item_defined_callback_ = cb;
   }
 
   // Defines a callback that will be used to override the behavior of the
   // print function. This is used in tests to collect print output. If the
   // callback is is_null() (the default) the output will be printed to the
   // console.
   const PrintCallback& print_callback() const { return print_callback_; }
   void set_print_callback(const PrintCallback& cb) { print_callback_ = cb; }
 
+  // A list of files that can call exec_script(). If the returned pointer is
+  // null, exec_script may be called from anywhere.
+  const std::set<SourceFile>* exec_script_whitelist() const {
+    return exec_script_whitelist_.get();
+  }
+  void set_exec_script_whitelist(scoped_ptr<std::set<SourceFile>> list) {
+    exec_script_whitelist_ = list.Pass();
+  }
+
  private:
   base::FilePath root_path_;
   std::string root_path_utf8_;
   base::FilePath secondary_source_path_;
   base::FilePath python_path_;
 
   SourceFile build_config_file_;
   SourceDir build_dir_;
   Args build_args_;
 
   ItemDefinedCallback item_defined_callback_;
   PrintCallback print_callback_;
 
+  scoped_ptr<std::set<SourceFile>> exec_script_whitelist_;
+
   BuildSettings& operator=(const BuildSettings& other);  // Disallow.
 };
 
 #endif  // TOOLS_GN_BUILD_SETTINGS_H_