Roll src/third_party/dart 05f3b12..a977273 (3 commits)

a977273 Re-allow the incremental compiler to load modules
7b33a8f [cfe] Fix type inference in map literals with spreads
864b22d [cfe] Add inference and type checks to if-elements in maps

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': '05f3b12960fbe1808d367df18b86095b1baed369',
+  'dart_revision': 'a977273262343d8fa2f8c5ae268be391f6087e30',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py