Roll src/third_party/dart 2195a70249..492df72739 (2 commits)

492df72739 Fix fasta test under windows
4ec9dbf1d0 Add set literal spread collection parsing support

DEPS

@@ -31,7 +31,7 @@ vars = {
   # Dart is: https://github.com/dart-lang/sdk/blob/master/DEPS.
   # You can use //tools/dart/create_updated_flutter_deps.py to produce
   # updated revision list of existing dependencies.
-  'dart_revision': '2195a70249cffd9e9347dab1fb5717a98481ecc8',
+  'dart_revision': '492df72739acb4e1c135d34eb75dfd676caa45ba',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py