gn: Support build directories outside the source tree.

tools/gn/setup.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/setup.h"
 
 #include <stdlib.h>
 
 #include <algorithm>
 #include <sstream>
@@ skipping 423 matching lines @@
   if (scheduler_.verbose_logging())
     scheduler_.Log("Using source root", FilePathToUTF8(root_path));
   build_settings_.SetRootPath(root_path);
 
   return true;
 }
 
 bool Setup::FillBuildDir(const std::string& build_dir, bool require_exists) {
   SourceDir resolved =
       SourceDirForCurrentDirectory(build_settings_.root_path()).
-          ResolveRelativeDir(build_dir);
+    ResolveRelativeDir(build_dir, build_settings_.root_path());
   if (resolved.is_null()) {
     Err(Location(), "Couldn't resolve build directory.",
         "The build directory supplied (\"" + build_dir + "\") was not valid.").
         PrintToStdout();
     return false;
   }
 
   if (scheduler_.verbose_logging())
     scheduler_.Log("Using build dir", resolved.value());
 
@@ skipping 91 matching lines @@
 
   // Root build file.
   const Value* root_value = dotfile_scope_.GetValue("root", true);
   if (root_value) {
     if (!root_value->VerifyTypeIs(Value::STRING, &err)) {
       err.PrintToStdout();
       return false;
     }
 
     Label root_target_label =
-        Label::Resolve(SourceDir("//"), Label(), *root_value, &err);
+        Label::Resolve(SourceDir("//"), Label(), *root_value,
+                       build_settings_.root_path(), &err);
     if (err.has_error()) {
       err.PrintToStdout();
       return false;
     }
 
     root_build_file_ = Loader::BuildFileForLabel(root_target_label);
   }
 
   // Build config file.
   const Value* build_config_value =
@@ skipping 37 matching lines @@
 }
 
 void DependentSetup::RunPreMessageLoop() {
   CommonSetup::RunPreMessageLoop();
 }
 
 bool DependentSetup::RunPostMessageLoop() {
   return CommonSetup::RunPostMessageLoop();
 }