Dart SDK roll for 2018/09/20 (flutter#6294)

46ec629 [vm/bytecode] Trigger JIT-compilation from interpreter
9f5aecb Introduce a new flag to the Dart Analysis Server: --ux-experiment-1 which changes analysis roots to the be the current set of priority files.
9f72b09 Convert resolver.dart to triple-slash comment style.
ee0a603 Fix checks for absence of concrete implementations of super-invoked members.
3a5b748 Optimize index data structure for search by supertype id.
af2fd41 Update more analyzer error codes to be generated from messages.yaml
0bbdd8f [build] Correctly rebase kernel-service output for depfile
cbf6067 [vm/fuzzer] Migrated driver from Python to Dart.
e95d944 [VM interpreter] Propagate error from invoked compiled function to interpreter caller.
05ba853 Cleanup fasta parser rewriter insert token methods
07a1f23 Improve parser recover to fix more code completion tests
ffa99b9 Update analyzer error code generation
fa0b38b Fix some constructor initializer code completion situations
2455141 Remove ClassElement.isSuperConstructorAccessible().
3263550 [vm] Decouple bytecode reading from compilation
e3dbea9 Convert declaration_resolver.dart to triple-slash comment style.
d32e93d Remove unused import.
4baa3ec Create a base class for non-error resolver test cases.
2e43557 Mark Kernel classes that were Dart mixin declarations

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': 'c688d0c0c3ad3dece3a79ce0e115d787a94707ea',
+  'dart_revision': '46ec62909684e2944b7599b3d268b5ad351f628a',
 
   'dart_args_tag': '1.4.4',
   'dart_async_tag': '2.0.8',

ci/licenses_golden/licenses_third_party

@@ -1,4 +1,4 @@
-Signature: dfbc023ceeca15d70ea76e125a481c0f
+Signature: 2bc2dadbb340855517114ebd927ca790
 
 UNUSED LICENSES:
 
@@ -5455,6 +5455,7 @@ FILE: ../../../third_party/dart/runtime/bin/typed_data_utils.cc
 FILE: ../../../third_party/dart/runtime/bin/typed_data_utils.h
 FILE: ../../../third_party/dart/runtime/include/dart_embedder_api.h
 FILE: ../../../third_party/dart/runtime/tools/dartfuzz/dartfuzz.dart
+FILE: ../../../third_party/dart/runtime/tools/dartfuzz/dartfuzz_test.dart
 FILE: ../../../third_party/dart/runtime/vm/base64.cc
 FILE: ../../../third_party/dart/runtime/vm/base64.h
 FILE: ../../../third_party/dart/runtime/vm/base64_test.cc