Add initial prototype for the GN meta-buildsystem.

tools/gn/value_extractors.h

Index: tools/gn/value_extractors.h
diff --git a/tools/gn/value_extractors.h b/tools/gn/value_extractors.h
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index 0000000000000000000000000000000000000000..556f44fd2ee6f52fa662eb9af00584d88a83ec84
--- /dev/null
+++ b/tools/gn/value_extractors.h
@@ -0,0 +1,57 @@
+// 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>
+
+#include "tools/gn/value.h"
+
+class Err;
+class Label;
+class SourceDir;
+class SourceFile;
+
+// Sets the error and returns false on failure.
+template<typename T, class Converter>
+bool ListValueExtractor(const Value& value, std::vector<T>* dest,
+                        Err* err,
+                        const Converter& converter) {
+  if (!value.VerifyTypeIs(Value::LIST, err))
+    return false;
+  const std::vector<Value>& input_list = value.list_value();
+  dest->resize(input_list.size());
+  for (size_t i = 0; i < input_list.size(); i++) {
+    if (!converter(input_list[i], &(*dest)[i], err))
+      return false;
+  }
+  return true;
+}
+
+// On failure, returns false and sets the error.
+bool ExtractListOfStringValues(const Value& value,
+                               std::vector<std::string>* dest,
+                               Err* err);
+
+// Looks for a list of source files relative to a given current dir.
+bool ExtractListOfRelativeFiles(const Value& value,
+                                const SourceDir& current_dir,
+                                std::vector<SourceFile>* files,
+                                Err* err);
+
+// Looks for a list of source directories relative to a given current dir.
+bool ExtractListOfRelativeDirs(const Value& value,
+                               const SourceDir& current_dir,
+                               std::vector<SourceDir>* dest,
+                               Err* err);
+
+bool ExtractListOfLabels(const Value& value,
+                         const SourceDir& current_dir,
+                         const Label& current_toolchain,
+                         std::vector<Label>* dest,
+                         Err* err);
+
+#endif  // TOOLS_GN_VALUE_EXTRACTORS_H_