Roll src/third_party/dart 270966b16044..171059d27689 (19 commits) (flutter#14558)

https://dart.googlesource.com/sdk.git/+log/270966b16044..171059d27689

git log 270966b16044..171059d27689 --date=short --first-parent --format='%ad %ae %s'
2019-12-18 nshahan@google.com [test_runner] Avoid potential errors using the wrong SDK fork in paths
2019-12-18 scheglov@google.com Remove AnalysisOptionsImpl.strongModeHints
2019-12-18 mfairhurst@google.com [nnbd_migration] Handle downcasting type arguments.
2019-12-18 bkonyi@google.com [ package:vm_service ] Fix issue where TimelineEvent objects never had any content
2019-12-18 alexmarkov@google.com [vm/bytecode] Cleanup support for old versions of bytecode format
2019-12-18 paulberry@google.com Migration: Re-architect FixBuilder to use the analyzer resolver.
2019-12-18 brianwilkerson@google.com Remove unnecessary uses of new in analysis_server
2019-12-18 brianwilkerson@google.com Remove unnecessary uses of const in analyzer_cli
2019-12-18 brianwilkerson@google.com Remove unnecessary uses of new in analysis_server_client
2019-12-18 nshahan@google.com [test_runner] Only skip analyzer configurations with NNBD on language_2
2019-12-18 sigmund@google.com Whitelist _2 suites as opted out from NNBD
2019-12-18 aam@google.com Reland "[vm, linux] Try to attach names to all VirtualMemory allocations using memfd."
2019-12-18 scheglov@google.com Remove StrongModeCode.DYNAMIC_INVOKE
2019-12-18 sjindel@google.com [vm] Don't require inputs to be _Smi in InlineByteArrayBaseStore in AOT.
2019-12-18 rnystrom@google.com Migrate corelib_2/regexp files to NNBD.
2019-12-18 sstrickl@google.com [vm] Reland "Weaken dwarf_stack_trace expected stack trace."
2019-12-18 dmitryas@google.com [cfe] Report an error if thrown expression isn't assignable to Object
2019-12-18 dmitryas@google.com [cfe] Fix compiler crashes on for-in iterables with Null type
2019-12-18 danny@tuppeny.com Update LSP spec URI and regenerate from spec

Created with:
  gclient setdep -r src/third_party/dart@171059d27689

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

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': '270966b160442f3ee16f99f9de18b263900c7050',
+  'dart_revision': '171059d2768967b8b17e8ce33f09ce413c63b69a',
 
   # 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

@@ -1,4 +1,4 @@
-Signature: 48939ac3d8120cff452043892bb7e0a3
+Signature: f1b01cca605a48a58c06e37f300d0e79
 
 UNUSED LICENSES: