gn: Support build directories outside the source tree.

tools/gn/label.cc

 // 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.
 
 #include "tools/gn/label.h"
 
 #include "base/logging.h"
 #include "tools/gn/err.h"
 #include "tools/gn/parse_tree.h"
 #include "tools/gn/value.h"
@@ skipping 26 matching lines @@
 
   // Don't allow directories to start with a single slash. All labels must be
   // in the source root.
   if (input[0] == '/' && (input.size() == 1 || input[1] != '/')) {
     *err = Err(input_value, "Label can't start with a single slash",
         "Labels must be either relative (no slash at the beginning) or be "
         "absolute\ninside the source root (two slashes at the beginning).");
     return false;
   }
 
-  *result = current_dir.ResolveRelativeDir(input);
+  *result = current_dir.ResolveRelativeDir(input, base::FilePath());
   return true;
 }
 
 // Given the separated-out target name (after the colon) computes the final
 // name, using the implicit name from the previously-generated
 // computed_location if necessary. The input_value is used only for generating
 // error messages.
 bool ComputeTargetNameFromDep(const Value& input_value,
                               const SourceDir& computed_location,
                               const base::StringPiece& input,
@@ skipping 204 matching lines @@
   }
   return ret;
 }
 
 std::string Label::GetUserVisibleName(const Label& default_toolchain) const {
   bool include_toolchain =
       default_toolchain.dir() != toolchain_dir_ ||
       default_toolchain.name() != toolchain_name_;
   return GetUserVisibleName(include_toolchain);
 }