Roll src/third_party/dart 5b21a43c556c..1bab476834dc (41 commits)

[skia-flutter-autoroll]

https://dart.googlesource.com/sdk.git/+log/5b21a43c556c..1bab476834dc

git log 5b21a43..1bab476 --date=short --first-parent --format='%ad %ae %s'
2020-03-20 asiva@google.com [VM/NNBD] - Make the null safety flag be isolate specific.
2020-03-20 nbosch@google.com Update to latest source_span
2020-03-20 bkonyi@google.com Revert "[ VM / Service ] Migrated Observatory service tests from package:unittest to package:test and package:expect."
2020-03-19 bkonyi@google.com [ VM / Service ] Migrated Observatory service tests from package:unittest to package:test and package:expect.
2020-03-19 rmacnak@google.com [observatory] Prepare for the future signature of Object.==.
2020-03-19 bkonyi@google.com [ package:dds ] Initial commit of the Dart Development Service, package:dds
2020-03-19 leafp@google.com Make StackTrace generally not nullable in migrated NNBD library.
2020-03-19 devoncarew@google.com [nnbd migration] move the docs for the NNBD migration tool
2020-03-19 zichangguo@google.com Revert "[dart:io] Fix hanging on zero-length datagram"
2020-03-19 scheglov@google.com Stop clearing evaluationResult for ConstVariableElement(s).
2020-03-19 brianwilkerson@google.com Add new relevance support to the OverrideContributor
2020-03-19 liama@google.com [test] Fix some nits in strong mode mirror tests
2020-03-19 scheglov@google.com Give 'filename' to attachment MultipartFile(s).
2020-03-19 rmacnak@google.com [observatory] Remove use of the default List constructor.
2020-03-19 zichangguo@google.com [dart:io] avoid http smuggling
2020-03-19 brianwilkerson@google.com Add relevance support to InheritedReferenceContributor
2020-03-19 brianwilkerson@google.com Consolidate relevance tests into a single directory
2020-03-19 liama@google.com [vm] Fix a bug in required param function subtyping
2020-03-19 joshualitt@google.com [dart2js] Make switch_equals_test nnbd.
2020-03-19 zichangguo@google.com [dart:io] Fix hanging on zero-length datagram
2020-03-19 asiva@google.com [Tests/NNBD] - Migrate initial set of isolate tests for NNBD.
2020-03-19 sra@google.com [dart2js] Remove _CastError and Rti.check
2020-03-19 srawlins@google.com Trim not useful bottoms off of the non/nullability stack traces
2020-03-19 liama@google.com [vm] Mark member signatures as not reflectable
2020-03-19 joshualitt@google.com [dart2js] Drop nullability when checking for simple types.
2020-03-19 rmacnak@google.com [vm] Require explicit loads and stores when using AcqRelAtomic.
2020-03-19 brianwilkerson@google.com Use the deprecated feature for static members
2020-03-19 rmacnak@google.com [vm] Fix data race on BackgroundCompiler::running.
2020-03-19 johnniwinther@google.com [cfe] Compute consolidated supertypes
2020-03-19 paulberry@google.com Migration: fix the descriptions of nullability nodes associated with parameters.
2020-03-19 brianwilkerson@google.com Perform new relevance computations for extension members
2020-03-19 vsm@google.com Revert "Revert "[dartdevc] record metrics""
2020-03-19 dmitryas@google.com [cfe] Report NNBD warnings as errors in strong mode
2020-03-19 paulberry@google.com Migration: preserve code references for nullability nodes with explicit types.
2020-03-19 sque@google.com [build] GN flag to use relative symlink to Xcode
2020-03-19 athom@google.com [beta] Support the beta channel in SDK scripts
2020-03-19 sra@google.com [dart2js] Add '--legacy-javascript' flag
2020-03-19 bkonyi@google.com [ VM ] Update lib_2/isolate tests to no longer use package:unittest
2020-03-19 regis@google.com [VM/nnbd] Normalize FutureOr when loading kernel file.
2020-03-18 alexmarkov@google.com [vm/nnbd] Specialize List.filled constructor invocations
2020-03-18 regis@google.com [VM/nnbd] Use correct top type in inline code for is-test.

Created with:
gclient setdep -r src/third_party/dart@1bab476834dc

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