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

utils/compiler/compiler.gyp

 # Copyright (c) 2012, 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.
 
 {
   'variables': {
     'dart_dir': '../..',
   },
   'targets': [
     {
       'target_name': 'dart2js',
       'type': 'none',
       'dependencies': [
         '../../runtime/dart-runtime.gyp:dart',
         'dart2js_files_stamp',
       ],
       'actions': [
         {
           'action_name': 'generate_snapshots',
           'inputs': [
             '<(PRODUCT_DIR)/<(EXECUTABLE_PREFIX)dart<(EXECUTABLE_SUFFIX)',
             '../../sdk/lib/_internal/sdk_library_metadata/lib/libraries.dart',
-            '<!@(["python", "../../tools/list_files.py", "\\.dart$", "../../runtime/lib", "../../sdk/lib/_internal/dartdoc"])',
+            '<!@(["python", "../../tools/list_files.py",  "relative", '
+                '"\\.dart$", '
+                '"../../runtime/lib", '
+                '"../../sdk/lib/_internal/dartdoc"])',
             'create_snapshot.dart',
             '<(SHARED_INTERMEDIATE_DIR)/dart2js_files.stamp',
             '../../tools/VERSION',
           ],
           'outputs': [
             '<(SHARED_INTERMEDIATE_DIR)/utils_wrapper.dart.snapshot',
             '<(SHARED_INTERMEDIATE_DIR)/dart2js.dart.snapshot',
           ],
           'action': [
             '<(PRODUCT_DIR)/<(EXECUTABLE_PREFIX)dart<(EXECUTABLE_SUFFIX)',
@@ skipping 10 matching lines @@
     # This target lists all the files in pkg/compiler,
     # and creates a single dart2js_files.stamp
     {
       'target_name': 'dart2js_files_stamp',
       'type': 'none',
       'actions': [
         {
           'action_name': 'make_dart2js_files_stamp',
           'inputs': [
             '../../tools/create_timestamp_file.py',
-            '<!@(["python", "../../tools/list_files.py", "\\.dart$",'
+            '<!@(["python", "../../tools/list_files.py", "relative", '
+                '"\\.dart$", '
                 ' "../../pkg/compiler/lib"])',
           ],
           'outputs': [
             '<(SHARED_INTERMEDIATE_DIR)/dart2js_files.stamp',
           ],
           'action': [
             'python', '../../tools/create_timestamp_file.py',
             '<@(_outputs)',
           ],
         },
       ],
     }
   ],
 }