Roll Dart SDK from 97cfd05b3cb3 to a37a4d42e53d (4 revisions) (flutter#22849)

https://dart.googlesource.com/sdk.git/+log/97cfd05b3cb3..a37a4d42e53d

2020-12-03 [email protected] Version 2.12.0-112.0.dev
2020-12-03 [email protected] Version 2.12.0-111.0.dev
2020-12-03 [email protected] Version 2.12.0-110.0.dev
2020-12-03 [email protected] Version 2.12.0-109.0.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 [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/+doc/master/autoroll/README.md

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': '97cfd05b3cb34c3e86ab22223b069fad74ebafaf',
+  'dart_revision': 'a37a4d42e53d504813874ab0ee05e94e77d30955',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py
@@ -156,7 +156,7 @@ deps = {
   # WARNING: Unused Dart dependencies in the list below till "WARNING:" marker are removed automatically - see create_updated_flutter_deps.py.
 
   'src/third_party/dart/third_party/pkg/args':
-   Var('dart_git') + '/args.git@139140125126661fac88c9aa5882165936d01c91',
+   Var('dart_git') + '/args.git@1.6.0',
 
   'src/third_party/dart/third_party/pkg/async':
    Var('dart_git') + '/async.git@695b3ac280f107c84adf7488743abfdfaaeea68f',

ci/licenses_golden/licenses_third_party

@@ -1,4 +1,4 @@
-Signature: a9de04379f69ec3212559677e2f03339
+Signature: f605a424bdfd7039cd2374cf2f518c6f
 
 UNUSED LICENSES:
 

tools/const_finder/.dart_tool/package_config.json

@@ -23,7 +23,7 @@
       "name": "args",
       "rootUri": "../../../../third_party/dart/third_party/pkg/args",
       "packageUri": "lib",
-      "languageVersion": "2.12"
+      "languageVersion": "2.3"
     },
     {
       "name": "collection",