gn: Support build directories outside the source tree.

tools/gn/path_output.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_PATH_OUTPUT_H_
 #define TOOLS_GN_PATH_OUTPUT_H_
 
 #include <iosfwd>
 #include <string>
 
@@ skipping 15 matching lines @@
  public:
   // Controls whether writing directory names include the trailing slash.
   // Often we don't want the trailing slash when writing out to a command line,
   // especially on Windows where it's a backslash and might be interpreted as
   // escaping the thing following it.
   enum DirSlashEnding {
     DIR_INCLUDE_LAST_SLASH,
     DIR_NO_LAST_SLASH,
   };
 
-  PathOutput(const SourceDir& current_dir, EscapingMode escaping);
+  PathOutput(const SourceDir& current_dir, const base::StringPiece& source_root,
+             EscapingMode escaping);
   ~PathOutput();
 
   // Read-only since inverse_current_dir_ is computed depending on this.
   EscapingMode escaping_mode() const { return options_.mode; }
 
   const SourceDir& current_dir() const { return current_dir_; }
 
   // Getter/setters for flags inside the escape options.
   bool inhibit_quoting() const { return options_.inhibit_quoting; }
   void set_inhibit_quoting(bool iq) { options_.inhibit_quoting = iq; }
@@ skipping 31 matching lines @@
 
   // Uses system slashes if convert_slashes_to_system_.
   std::string inverse_current_dir_;
 
   // Since the inverse_current_dir_ depends on some of these, we don't expose
   // this directly to modification.
   EscapeOptions options_;
 };
 
 #endif  // TOOLS_GN_PATH_OUTPUT_H_