Make list_files.py and list_dart_files.py return absolute paths for GN

BUILD.gn

 # Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 # This target will be built if no target is specified when invoking ninja.
 group("default") {
   deps = [
     ":runtime",
   ]
 }
@@ skipping 52 matching lines @@
     "utils/dartanalyzer:generate_dartanalyzer_snapshot",
     "utils/dartanalyzer:generate_summary_spec",
     "utils/dartanalyzer:generate_summary_strong",
     "utils/dartdevc",
     "utils/dartdoc",
     "utils/dartfmt",
     "utils/pub",
   ]
 
   sdk_lib_files = exec_script("tools/list_dart_files.py",
-                              [ rebase_path("sdk/lib") ],
+                              [ "absolute", rebase_path("sdk/lib") ],
                               "list lines")
 
   preamble_files =
       exec_script("tools/list_files.py",
                   [
+                    "absolute",
                     "",
                     rebase_path("sdk/lib/_internal/js_runtime/lib/preambles"),
                   ],
                   "list lines")
 
   sdk_bin_files = exec_script("tools/list_files.py",
                               [
+                                "absolute",
                                 "",
                                 rebase_path("sdk/bin"),
                               ],
                               "list lines")
 
-  inputs = rebase_path(sdk_lib_files, "", "sdk/lib") +
-           rebase_path(preamble_files, "", "sdk/lib") +
-           rebase_path(sdk_bin_files, "", "sdk/bin") +
+  inputs = sdk_lib_files + preamble_files + sdk_bin_files +
            [
              "sdk/lib/dart_client.platform",
              "sdk/lib/dart_server.platform",
              "sdk/lib/dart_shared.platform",
              "$root_gen_dir/dart2js.dart.snapshot",
              "$root_gen_dir/utils_wrapper.dart.snapshot",
              "$root_gen_dir/pub.dart.snapshot",
              "$root_gen_dir/dartanalyzer.dart.snapshot",
              "$root_gen_dir/dartdevc.dart.snapshot",
              "$root_gen_dir/dartfmt.dart.snapshot",
@@ skipping 54 matching lines @@
   deps = [
     ":create_sdk",
   ]
 }
 
 group("samples") {
   deps = [
     "runtime/bin:sample_extension",
   ]
 }