Roll Dart SDK from f997d62 to 20bf2fc (18 revisions) (#19735)

https://dart.googlesource.com/sdk.git/+log/f997d62a6d29..20bf2fcf5670

2020-07-14 kustermann@google.com [vm/compiler] Make precompiler prune invocation dispatchers the same way we do for regular/closure functions
2020-07-14 whesse@google.com [build] Change flutter-engine patch for async to use updated Dart SDK hash
2020-07-14 sortie@google.com Roll benchmarks-internal 78e4b5975ab4..9bfe209a53a5
2020-07-14 kustermann@google.com [vm] Remove unused function
2020-07-14 jakemac@google.com update async in the sdk, add flutter engine patch
2020-07-14 srawlins@google.com analyzer: Move tests for 9 codes to diagnostics/
2020-07-14 scheglov@google.com Prepare to publish analyzer 0.39.13
2020-07-14 regis@google.com [VM/nnbd] Class Future may be used for type normalization before it is cached in the object store.
2020-07-14 bkonyi@google.com [ package:dds ] Fixed expression evaluator expecting a double-nested 'result' from an external 'compileExpression' implementation
2020-07-14 nshahan@google.com [ddc] Copy more .dill files to packaged sdk
2020-07-13 nbosch@google.com Update to latest package:matcher
2020-07-13 aam@google.com [vm/bytecode] Ensure class is allocate-finalized before instantiated by bytecode runtime calls.
2020-07-13 kenzieschmoll@google.com Remove dart:io dep from utils.dart and add conditional imports for File
2020-07-13 bkonyi@google.com [ package:dds ] Fix issue where `StateError` could be raised when a client disconnects from DDS after the VM service has shutdown
2020-07-13 nshahan@google.com [ddc] Inline the sound null safety flag
2020-07-13 scheglov@google.com Support for data attachments to OperationPerformance.
2020-07-13 scheglov@google.com Instrument getAnalysisOptions() for Cider.
2020-07-13 scheglov@google.com Remove deprecated CiderOperationPerformance.

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

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': 'f997d62a6d29fa23ca140a60bba987fac7251c56',
+  'dart_revision': '20bf2fcf567074d087d977cfbfb469e7fe766023',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py
@@ -170,7 +170,7 @@ deps = {
    Var('dart_git') + '/args.git' + '@' + Var('dart_args_tag'),
 
   'src/third_party/dart/third_party/pkg/async':
-   Var('dart_git') + '/async.git@e0c41e0c1fb70ba606dc81335c981af7c00987c6',
+   Var('dart_git') + '/async.git@5a4373458bfc902e4a4064427c619c2b41783f0d',
 
   'src/third_party/dart/third_party/pkg/bazel_worker':
    Var('dart_git') + '/bazel_worker.git@26680d5e249b249c7216ab2fed0ac8ed4ee285c5',
@@ -245,7 +245,7 @@ deps = {
    Var('dart_git') + '/markdown.git@dd150bb64c5f3b41d31f20f399ae2a855f7f8c00',
 
   'src/third_party/dart/third_party/pkg/matcher':
-   Var('dart_git') + '/matcher.git@af4fe7daf8e94a46981e4f072872be550a6969e9',
+   Var('dart_git') + '/matcher.git@8f8d965933c94a489b1a39e20d558a32841bfa5b',
 
   'src/third_party/dart/third_party/pkg/mime':
    Var('dart_git') + '/mime.git@179b5e6a88f4b63f36dc1b8fcbc1e83e5e0cd3a7',

ci/licenses_golden/licenses_third_party

@@ -1,4 +1,4 @@
-Signature: e575ad17a116204a303fd87eeb77de26
+Signature: 85932205c4f2a2abd9ccf1fb28e2a719
 
 UNUSED LICENSES: