Make GN --as=output relative to the root build directory.

tools/gn/commands.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/commands.h"
 
 #include "base/command_line.h"
 #include "tools/gn/builder.h"
 #include "tools/gn/filesystem_utils.h"
 #include "tools/gn/item.h"
@@ skipping 305 matching lines @@
 
 void PrintTargetsAsOutputs(bool indent,
                            const std::vector<const Target*>& targets) {
   if (targets.empty())
     return;
 
   // Grab the build settings from a random target.
   const BuildSettings* build_settings =
       targets[0]->settings()->build_settings();
 
-  SourceDir current_dir = SourceDirForCurrentDirectory(
-      build_settings->root_path());
   for (const Target* target : targets) {
     // Use the link output file if there is one, otherwise fall back to the
     // dependency output file (for actions, for example).
     OutputFile output_file = target->link_output_file();
     if (output_file.value().empty())
       output_file = target->dependency_output_file();
 
     SourceFile output_as_source =
         output_file.AsSourceFile(build_settings);
-    std::string result = RebasePath(output_as_source.value(), current_dir,
+    std::string result = RebasePath(output_as_source.value(),
+                                    build_settings->build_dir(),
                                     build_settings->root_path_utf8());
     if (indent)
       OutputString("  ");
     OutputString(result);
     OutputString("\n");
   }
 }
 
 }  // namespace
 
@@ skipping 146 matching lines @@
   }
 }
 
 void FilterAndPrintTargetSet(bool indent,
                              const std::set<const Target*>& targets) {
   std::vector<const Target*> target_vector(targets.begin(), targets.end());
   FilterAndPrintTargets(indent, &target_vector);
 }
 
 }  // namespace commands