Reference written files relatively when possible.

tools/gn/ninja_build_writer.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/ninja_build_writer.h"
 
 #include <fstream>
 #include <map>
 
 #include "base/command_line.h"
@@ skipping 136 matching lines @@
 
   // This rule will regenerate the ninja files when any input file has changed,
   // or is missing.
   out_ << "build build.ninja";
 
   // Other files read by the build.
   EscapeOptions path_escaping;
   path_escaping.mode = ESCAPE_NINJA_COMMAND;
   std::vector<SourceFile> written_files = g_scheduler->GetWrittenFiles();
   for (const auto& written_file : written_files)
-    out_ << " " <<
-        EscapeString(FilePathToUTF8(build_settings_->GetFullPath(written_file)),
-                     path_escaping, nullptr);
+    out_ << " " << EscapeString(RebasePath(written_file.value(),
+        build_settings_->build_dir(), build_settings_->root_path_utf8()),
+        path_escaping, nullptr);
 
   out_ << ": gn\n"
        << "  generator = 1\n"
        << "  depfile = build.ninja.d\n";
 
   // Input build files. These go in the ".d" file. If we write them as
   // dependencies in the .ninja file itself, ninja will expect the files to
   // exist and will error if they don't. When files are listed in a depfile,
   // missing files are ignored.
   dep_out_ << "build.ninja:";
@@ skipping 155 matching lines @@
   EscapeOptions ninja_escape;
   ninja_escape.mode = ESCAPE_NINJA;
 
   // Escape for special chars Ninja will handle.
   std::string escaped = EscapeString(phony_name, ninja_escape, nullptr);
 
   out_ << "build " << escaped << ": phony ";
   path_output_.WriteFile(out_, target_file);
   out_ << std::endl;
 }