Dart SDK roll for 2019-01-09

f4986cc Fixed a couple of typos, including LaTeX error
68f77fa Specify that extending or implementing Function does nothing.
0f1b943 Use 'no-' prefix to disable an experiment.
de85d16 Implement DillClass.supertype
2bc015b Remove dependency on TypeEnvironment.hierarchy
7ba1997 Save transient state
2bb2f5e Simplify ClassHierarchyBuilder.getNode
34afa49 Merge interfaces only when necessary
1dc920e Change names to reflect merge isn't used only for superclasses

Author: bkonyi

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': '50ea6344f5a85493b57df086bd70b686ca2baaf6',
+  'dart_revision': 'f4986cc78ddd884e60e7274c44f31dbcd990b912',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py