Add GN variables for controlling header checking.

tools/gn/value_extractors.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_VALUE_EXTRACTORS_H_
 #define TOOLS_GN_VALUE_EXTRACTORS_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 27 matching lines @@
                                Err* err);
 
 // Extracts the list of labels and their origins to the given vector. Only the
 // labels are filled in, the ptr for each pair in the vector will be null.
 bool ExtractListOfLabels(const Value& value,
                          const SourceDir& current_dir,
                          const Label& current_toolchain,
                          LabelTargetVector* dest,
                          Err* err);
 
-// Extracts the list of labels and their origins to the given vector. Only the
-// labels are filled in, the ptr for each pair in the vector will be null. Sets
-// an error and returns false if a label is maformed or there are duplicates.
+// Extracts the list of labels and their origins to the given vector. For the
+// version taking Label*Pair, only the labels are filled in, the ptr for each
+// pair in the vector will be null. Sets an error and returns false if a label
+// is maformed or there are duplicates.
 bool ExtractListOfUniqueLabels(const Value& value,
                                const SourceDir& current_dir,
                                const Label& current_toolchain,
+                               UniqueVector<Label>* dest,
+                               Err* err);
+bool ExtractListOfUniqueLabels(const Value& value,
+                               const SourceDir& current_dir,
+                               const Label& current_toolchain,
                                UniqueVector<LabelConfigPair>* dest,
                                Err* err);
 bool ExtractListOfUniqueLabels(const Value& value,
                                const SourceDir& current_dir,
                                const Label& current_toolchain,
                                UniqueVector<LabelTargetPair>* dest,
                                Err* err);
 
 bool ExtractRelativeFile(const BuildSettings* build_settings,
                          const Value& value,
                          const SourceDir& current_dir,
                          SourceFile* file,
                          Err* err);
 
 #endif  // TOOLS_GN_VALUE_EXTRACTORS_H_