Roll Dart SDK from 2e838b7b4503 to 5e8b31a5fa48 (2 revisions) (#21054)

https://dart.googlesource.com/sdk.git/+log/2e838b7b4503..5e8b31a5fa48

2020-09-09 dart-luci-ci-builder@dart-ci.iam.gserviceaccount.com Version 2.10.0-109.0.dev
2020-09-09 dart-luci-ci-builder@dart-ci.iam.gserviceaccount.com Version 2.10.0-108.0.dev

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/+doc/master/autoroll/README.md

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': '2e838b7b4503f055da8b90f8bc5c6c48f630812e',
+  'dart_revision': '5e8b31a5fa48ab8cd86beb76a7530dd99dc568b0',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py

ci/licenses_golden/licenses_third_party

-Signature: 1c09ff764f7d673f43411d160d4d63af
+Signature: abc81395f01d5e7a718dc8c5c3765546
 
 UNUSED LICENSES: