Roll src/third_party/dart 896c053803..b31df28d72 (10 commits)

dart-lang/sdk@b31df28d72 [dart:io] Retain the stack trace on some native socket errors
dart-lang/sdk@22866b6a19 Add test of ambiguous exports to verify an edge case
dart-lang/sdk@a9f6e0302b [vm/compiler] Unify IsRedundant for JIT/AOT bounds checks
dart-lang/sdk@63a1478f5f [dart:io] Handle http timeout race
dart-lang/sdk@9eb2e8d111 Stop reporting duplicate diagnostics for other ambiguous extensions
dart-lang/sdk@1f7e6370b4 Migration: store decorated type parameter bounds separately from other element decorated types.
dart-lang/sdk@c0d1dedd78 [vm] Disable inlining of _StringBase._createOneByteString
dart-lang/sdk@92562dc5a5 Fix hints in nnbd_migration package.
dart-lang/sdk@e86ce41bcf Rename a hint code to be consistent with similar codes
dart-lang/sdk@81569e5fe3 Ignore ErrorToken when locating previous n tokens for completion ranking

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': '896c053803a1699686941cf5b7542b8fcaa67e3e',
+  'dart_revision': 'b31df28d721156b041c3dd9ded7b304503177ee6',
 
   # 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: b8cb5dcf981bc89ba663c7c188cc7159
+Signature: fecb9bdc827a89ac8663b885360b1f50
 
 UNUSED LICENSES:
 
@@ -4751,6 +4751,7 @@ FILE: ../../../third_party/dart/runtime/vm/compiler/asm_intrinsifier_arm.cc
 FILE: ../../../third_party/dart/runtime/vm/compiler/asm_intrinsifier_arm64.cc
 FILE: ../../../third_party/dart/runtime/vm/compiler/asm_intrinsifier_ia32.cc
 FILE: ../../../third_party/dart/runtime/vm/compiler/asm_intrinsifier_x64.cc
+FILE: ../../../third_party/dart/runtime/vm/compiler/backend/bce_test.cc
 FILE: ../../../third_party/dart/runtime/vm/compiler/backend/block_builder.h
 FILE: ../../../third_party/dart/runtime/vm/compiler/backend/flow_graph_checker.cc
 FILE: ../../../third_party/dart/runtime/vm/compiler/backend/flow_graph_checker.h