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

tools/list_dart_files.py

Index: tools/list_dart_files.py
diff --git a/tools/list_dart_files.py b/tools/list_dart_files.py
index 60d2295652e1ea38e99094624bfd21cf3266bcfc..7a9ee8ab6c00564ead9a672d99c22f7dba48f17c 100755
--- a/tools/list_dart_files.py
+++ b/tools/list_dart_files.py
@@ -5,8 +5,12 @@
 
 """Tool for listing Dart source files.
 
+If the first argument is 'relative', the script produces paths relative to the
+current working directory. If the first argument is 'absolute', the script
+produces absolute paths.
+
 Usage:
-  python tools/list_dart_files.py <directory> <root directory pattern>
+  python tools/list_dart_files.py {absolute, relative} <directory> <pattern>
 """
 
 import os
@@ -15,11 +19,16 @@ import sys
 
 
 def main(argv):
-  directory = argv[1]
+  mode = argv[1]
+  if mode not in ['absolute', 'relative']:
+    raise Exception("First argument must be 'absolute' or 'relative'")
+  directory = argv[2]
+  if mode in 'absolute' and not os.path.isabs(directory):
+    directory = os.path.realpath(directory)
 
   pattern = None
-  if len(argv) > 2:
-    pattern = re.compile(argv[2])
+  if len(argv) > 3:
+    pattern = re.compile(argv[3])
 
   for root, directories, files in os.walk(directory):
     # We only care about actual source files, not generated code or tests.
@@ -34,7 +43,10 @@ def main(argv):
 
     for filename in files:
       if filename.endswith('.dart') and not filename.endswith('_test.dart'):
-        fullname = os.path.relpath(os.path.join(root, filename))
+        if mode in 'absolute':
+          fullname = os.path.join(directory, root, filename)
+        else:
+          fullname = os.path.relpath(os.path.join(root, filename))
         fullname = fullname.replace(os.sep, '/')
         print fullname