Roll dart to 52afcba (#4905)

* Roll to 59d8596

Changes since last roll:
```
59d8596 [fasta] Do new/const insertion in simple cases
4c0a09b [vm-service] Add setFlag.
bed5deb Callable object support in Analyzer and DDC.
a1e4d8e Don't do implicit new/const code generation with --preview-dart-2 enabled.
49558b9 Fixed MessageChannel receiveing messages on ports. Removed pkg browser from tests.
e150bf6 Fix tests for missing required SDK libraries on Windows.
b970d83 Update type_representation_test to test strong mode types
85d5812 Port type_representation_test to work with kernel
8504808 Remove Dart 2 errors in package:js_ast
a6a2152 Add runtime type representation for void
477a773 [fidl] Port Dart runtime to FIDL2.
d46dd1b fix error message for dcalls on null
af22f6a Track calls to 'pub get' from analysis_server
8d689fc step 4 of ??: add omit-implicit-checks and preview-dart-2 flags, strong-mode defaults to include implicit checks.
f201ace Check for missing required libraries dart:core and dart:async.
d53291d Fix MockErrorCode after adding isUnresolvedIdentifier.
b05ba71 [VM runtime] Minor clean up of type test with non-function type object.
ce1d524 Don't remove unused imports when there are unresolved symbols.
ad9afa1 Add the isUnresolvedIdentifier flag for ErrorCode.
14806df Make correction parameter optional named in ErrorCode and subclasses.
98f627f Issue 32708. Make GenericFunctionTypeElementForLink implement GenericFunctionTypeElementImpl.
3306aab Fix for type inference from instance creation arguments.
055dfad Fix the test to determine whether a library is in the SDK
506ac7f Rework linker type inference using ExprBuilder.
494b861 Further prep work for #32525.
7d90df4 [Kernel, VM runtime] Hook up bool checks in strong mode (fixes #32336). Update kernel status file.
```

* Update license hash. No changes to licenses.

* Roll to pick up SIGTTOU fix.

* Update license hash. No changes to licenses

Author: aam

DEPS

@@ -31,7 +31,7 @@ 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': '4da52281aa35b6c1951b3e269a6934412b15b105',
+  'dart_revision': '52afcba357ad398e8c24f3e3363ac6ff5293df63',
 
   'dart_args_tag': '1.4.1',
   'dart_async_tag': '2.0.6',

travis/licenses_golden/licenses_third_party

@@ -1,4 +1,4 @@
-Signature: 240f392a30cdf33f0ddff5fc2cf9241b
+Signature: 391179c630438133ec3f2d4060984728
 
 UNUSED LICENSES: