Add initial prototype for the GN meta-buildsystem.

tools/gn/string_utils.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_STRING_UTILS_H_
+#define TOOLS_GN_STRING_UTILS_H_
+
+#include "base/strings/string_piece.h"
+
+class Err;
+class Scope;
+class Token;
+class Value;
+
+inline std::string operator+(const std::string& a, const base::StringPiece& b) {
+  std::string ret;
+  ret.reserve(a.size() + b.size());
+  ret.assign(a);
+  ret.append(b.data(), b.size());
+  return ret;
+}
+
+inline std::string operator+(const base::StringPiece& a, const std::string& b) {
+  std::string ret;
+  ret.reserve(a.size() + b.size());
+  ret.assign(a.data(), a.size());
+  ret.append(b);
+  return ret;
+}
+
+// Unescapes and expands variables in the given literal, writing the result
+// to the given value. On error, sets |err| and returns false.
+bool ExpandStringLiteral(Scope* scope,
+                         const Token& literal,
+                         Value* result,
+                         Err* err);
+
+// Removes the given prefix from the string. Asserts if the string does
+// not have the given prefix.
+//
+// Note: could potentially return a StringPiece into the str.
+std::string RemovePrefix(const std::string& str, const std::string& prefix);
+
+// Appends the given string piece to the given string. This avoids an
+// intermediate copy.
+inline void AppendStringPiece(std::string* dest,
+                              const base::StringPiece& piece) {
+  dest->append(piece.data(), piece.size());
+}
+
+#endif  // TOOLS_GN_STRING_UTILS_H_