Use list_dart_files.py instead of list_files.py in GN build.

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 48 matching lines @@
     "utils/compiler:dart2js",
     "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_files.py",
-      ["\\.dart\$", rebase_path("sdk/lib")],
+  sdk_lib_files = exec_script("tools/list_dart_files.py",
+      [rebase_path("sdk/lib")],
       "list lines")
 
   preamble_files = exec_script("tools/list_files.py",
       ["", rebase_path("sdk/lib/_internal/js_runtime/lib/preambles")],
       "list lines")
 
   sdk_bin_files = exec_script("tools/list_files.py",
       ["", rebase_path("sdk/bin")],
       "list lines")
 
@@ skipping 67 matching lines @@
   deps = [
     ":create_sdk"
   ]
 }
 
 group("samples") {
   deps = [
     "runtime/bin:sample_extension"
   ]
 }