Make list_files.py and list_dart_files.py return absolute paths

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..39ab36555cc4d0ac258fc5b7244a77f43ac1b376 100755
--- a/tools/list_dart_files.py
+++ b/tools/list_dart_files.py
@@ -16,6 +16,8 @@ import sys
 
 def main(argv):
   directory = argv[1]
+  if not os.path.isabs(directory):
+    directory = os.path.realpath(directory)
 
   pattern = None
   if len(argv) > 2:
@@ -34,7 +36,7 @@ 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))
+        fullname = os.path.join(directory, root, filename)
         fullname = fullname.replace(os.sep, '/')
         print fullname