Add initial prototype for the GN meta-buildsystem.

tools/gn/input_conversion.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_INPUT_CONVERSION_H_
+#define TOOLS_GN_INPUT_CONVERSION_H_
+
+#include <string>
+
+class Err;
+class ParseNode;
+class Value;
+
+// Converts the given input string (is read from a file or output from a
+// script) to a Value. Conversions as specified in the input_conversion string
+// will be performed. The given origin will be used for constructing the
+// resulting Value.
+//
+// If the conversion string is invalid, the error will be set and an empty
+// value will be returned.
+Value ConvertInputToValue(const std::string& input,
+                          const ParseNode* origin,
+                          const Value& input_conversion_value,
+                          Err* err);
+
+#endif  // TOOLS_GN_INPUT_CONVERSION_H_