Roll src/third_party/dart 09a0b04..ae3973d (1 commits) (#14501)

https://dart.googlesource.com/sdk.git/+log/09a0b040dd9b..ae3973da4023

git log 09a0b04..ae3973d --date=short --first-parent --format='%ad %ae %s'
2019-12-14 scheglov@google.com Use FeatureSetProvider in AnalysisDriver.

Created with:
  gclient setdep -r src/third_party/dart@ae3973da4023

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 dart-vm-team@google.com 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: dart-vm-team@google.com

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': '09a0b040dd9b175d224a538527b0c4be096a271d',
+  'dart_revision': 'ae3973da40237d038e3afa5fd525a1b33ee543ed',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py