gn: Support build directories outside the source tree.

tools/gn/label.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_LABEL_H_
 #define TOOLS_GN_LABEL_H_
 
 #include "base/containers/hash_tables.h"
 #include "build/build_config.h"
 #include "tools/gn/source_dir.h"
@@ skipping 18 matching lines @@
   // Makes a label with an empty toolchain.
   Label(const SourceDir& dir, const base::StringPiece& name);
   ~Label();
 
   // Resolives a string from a build file that may be relative to the
   // current directory into a fully qualified label. On failure returns an
   // is_null() label and sets the error.
   static Label Resolve(const SourceDir& current_dir,
                        const Label& current_toolchain,
                        const Value& input,
+                       const base::FilePath& source_root,
                        Err* err);
 
   bool is_null() const { return dir_.is_null(); }
 
   const SourceDir& dir() const { return dir_; }
   const std::string& name() const { return name_; }
 
   const SourceDir& toolchain_dir() const { return toolchain_dir_; }
   const std::string& toolchain_name() const { return toolchain_name_; }
 
@@ skipping 77 matching lines @@
 }
 #endif  // COMPILER...
 
 }  // namespace BASE_HASH_NAMESPACE
 
 inline void swap(Label& lhs, Label& rhs) {
   lhs.swap(rhs);
 }
 
 #endif  // TOOLS_GN_LABEL_H_