gn: Support build directories outside the source tree.

tools/gn/build_settings.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_BUILD_SETTINGS_H_
 #define TOOLS_GN_BUILD_SETTINGS_H_
 
 #include <map>
 
 #include "base/basictypes.h"
@@ skipping 39 matching lines @@
 
   const SourceFile& build_config_file() const { return build_config_file_; }
   void set_build_config_file(const SourceFile& f) { build_config_file_ = f; }
 
   // The build directory is the root of all output files. The default toolchain
   // files go into here, and non-default toolchains will have separate
   // toolchain-specific root directories inside this.
   const SourceDir& build_dir() const { return build_dir_; }
   void SetBuildDir(const SourceDir& dir);
 
-  // The inverse of relative_build_dir, ending with a separator.
-  // Example: relative_build_dir_ = "out/Debug/" this will be "../../"
-  const std::string& build_to_source_dir_string() const {
-    return build_to_source_dir_string_;
-  }
-
   // The build args are normally specified on the command-line.
   Args& build_args() { return build_args_; }
   const Args& build_args() const { return build_args_; }
 
   // Returns the full absolute OS path cooresponding to the given file in the
   // root source tree.
   base::FilePath GetFullPath(const SourceFile& file) const;
   base::FilePath GetFullPath(const SourceDir& dir) const;
 
   // Returns the absolute OS path inside the secondary source path. Will return
@@ skipping 16 matching lines @@
   void set_print_callback(const PrintCallback& cb) { print_callback_ = cb; }
 
  private:
   base::FilePath root_path_;
   std::string root_path_utf8_;
   base::FilePath secondary_source_path_;
   base::FilePath python_path_;
 
   SourceFile build_config_file_;
   SourceDir build_dir_;
-  std::string build_to_source_dir_string_;
   Args build_args_;
 
   ItemDefinedCallback item_defined_callback_;
   PrintCallback print_callback_;
 
   BuildSettings& operator=(const BuildSettings& other);  // Disallow.
 };
 
 #endif  // TOOLS_GN_BUILD_SETTINGS_H_