Support more configurability in GN toolchains

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;
@@ skipping 30 matching lines @@
 // 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());
 }
 
+// Removes the trailing slash from the given string. This asserts that either
+// the string is empty or it ends with a slash (normally used to process
+// directories).
+void TrimTrailingSlash(std::string* str);
+
 #endif  // TOOLS_GN_STRING_UTILS_H_