Roll src/third_party/dart 1db1a837f8c9..cfca5ea9f2e9 (2 commits) (flutter#14667)

https://dart.googlesource.com/sdk.git/+log/1db1a837f8c9..cfca5ea9f2e9

git log 1db1a837f8c9..cfca5ea9f2e9 --date=short --first-parent --format='%ad %ae %s'
2019-12-21 [email protected] Fix NPE when describing a function in the info builder
2019-12-21 [email protected] Issue 39880. Resolve extension method invocations on null literals.

Created with:
  gclient setdep -r src/third_party/dart@cfca5ea9f2e9

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/dart-sdk-flutter-engine
Please CC [email protected] on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

Bug: None
Tbr: [email protected]

Author: skia-flutter-autoroll

DEPS

@@ -34,7 +34,7 @@ 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': '1db1a837f8c9e7e4e12c968efd98510527feae6b',
+  'dart_revision': 'cfca5ea9f2e996b4ec1f4d546fba89bfb783cd50',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py