Roll Dart SDK from 1f7dd915f40a to 0e52b2abe517 (2 revisions) (#23228)

https://dart.googlesource.com/sdk.git/+log/1f7dd915f40a..0e52b2abe517

2020-12-21 dart-luci-ci-builder@dart-ci.iam.gserviceaccount.com Version 2.12.0-171.0.dev
2020-12-21 dart-luci-ci-builder@dart-ci.iam.gserviceaccount.com Version 2.12.0-170.0.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': '1f7dd915f40ace48b466a55a8d4a57da04b67ebe',
+  'dart_revision': '0e52b2abe517d18192dfc7ffa2440d2e936bc465',
 
   # 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: 4e9e4c15524013d0d7bd4380045f3a8f
+Signature: b6b1d2bec5eaf52a287d86a280dd107b
 
 UNUSED LICENSES: