Roll src/third_party/dart 7d8ffe0daf..571ea80e11 (3 commits)

571ea80e11 [vm/compiler] added assert to kernel flowgraph builder
b88e6dd910 Fix the type argument on the deep flattening spread test.
62df51cb34 Eliminate uses of old AST node types from parts of the analyzer

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': '7d8ffe0daf8148dd281884ec3911f1274e21f0af',
+  'dart_revision': '571ea80e1101e706980ea8aefa7fc18a0c8ba2ec',
 
   # 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

-Signature: 1405abeaed1a76feefc683d14369d056
+Signature: 4a8dfa2afe659f0a6057032c092f7496
 
 UNUSED LICENSES: