Roll src/third_party/dart 81d4cc6bc99a..fd20c7b92bb8 (31 commits)

[skia-flutter-autoroll]

https://dart.googlesource.com/sdk.git/+log/81d4cc6bc99a..fd20c7b92bb8

git log 81d4cc6..fd20c7b --date=short --first-parent --format='%ad %ae %s'
2020-02-20 regis@google.com [VM/nnbd] Print nullability of types by default.
2020-02-20 kustermann@google.com [vm/concurrency] Share [Heap] and [SharedClassTable] between all isolates within one isolate group
2020-02-20 regis@google.com Reland "[VM/runtime] Fix type tests with LHS FutureOr (fixes #38906)."
2020-02-20 kustermann@google.com Reland "[vm/concurrency] Remove redundant isolates list, ensure shutdown procedure waits until the isolates actually got deleted"
2020-02-20 srujzs@google.com Remove unnecessary null check in getPropertyValue
2020-02-20 alexmarkov@google.com [nnbd/test tool] Add test configurations for NNBD strong mode for the VM
2020-02-20 rmacnak@google.com [build] Fix warnings in newer versions of Clang.
2020-02-20 alexmarkov@google.com [nnbd/vm/corelib] Fixes in VM core libraries for NNBD strong mode
2020-02-20 paulberry@google.com Migration: fix handling of part files.
2020-02-20 scheglov@google.com Extract YieldStatementResolver.
2020-02-20 markzipan@google.com [dartdevc] Adding performance optimizations for common legacy cases.
2020-02-20 devoncarew@google.com [dartdev] tweak the help text for the pub and format commands
2020-02-20 srujzs@google.com Fix multi-line error handling in analyze.dart
2020-02-20 scheglov@google.com Extract YIELD_OF_INVALID_TYPE tests.
2020-02-20 rmacnak@google.com Reland "[observatory] Display isolate groups."
2020-02-20 kevmoo@google.com update_homebrew: fix single audit error
2020-02-20 kevmoo@google.com update_homebrew: fix Dart homepage url
2020-02-20 rmacnak@google.com [observatory] Fix race in getCpuProfileTimeline.
2020-02-20 brianwilkerson@google.com Replace "generates" with "produces" in the diagnostic docs for consistency
2020-02-20 keertip@google.com Add a resolver for resolution of a single file.
2020-02-20 jensj@google.com Revert "[parser] New syntax for null aware index"
2020-02-20 dmitryas@google.com [cfe] Report errors on case expressions without primitive equality
2020-02-20 sstrickl@google.com [tests] Change the test we use to detect issues with instruction deduplication.
2020-02-20 sortie@google.com [dart:io] Throw StateError in meaningless getters on detached processes.
2020-02-20 vegorov@google.com [vm/snapshot] Add root names into write_v8_snapshot_profile_to output
2020-02-20 johnniwinther@google.com [cfe] Add option for agnostic nnbd mode
2020-02-20 jensj@google.com [parser] New syntax for null aware index
2020-02-20 askesc@google.com [vm/aot] Use the NOTFP register for the global dispatch table on ARM.
2020-02-20 askesc@google.com [vm] Free up NOTFP register on ARM in precompiled mode.
2020-02-20 johnniwinther@google.com [cfe] Add test for issue 40512
2020-02-20 rnystrom@google.com Change indexOf() and lastIndexOf() back to Object.

Created with:
gclient setdep -r src/third_party/dart@fd20c7b92bb8

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