Migrate async tests to strong

pkg/dev_compiler/test/not_yet_strong_tests.dart

 import 'dart:collection';
 
 /// The set of tests that are not yet strong mode safe.
 final notYetStrongTests = new HashSet<String>.from([
   'language/abstract_exact_selector_test_01_multi',
   'language/abstract_factory_constructor_test_00_multi',
   'language/abstract_getter_test_01_multi',
   'language/abstract_runtime_error_test_01_multi',
   'language/abstract_runtime_error_test_02_multi',
   'language/abstract_runtime_error_test_03_multi',
@@ skipping 2072 matching lines @@
   'corelib/symbol_reserved_word_test_07_multi',
   'corelib/symbol_reserved_word_test_08_multi',
   'corelib/symbol_reserved_word_test_10_multi',
   'corelib/symbol_reserved_word_test_11_multi',
   'corelib/symbol_test_01_multi',
   'corelib/symbol_test_02_multi',
   'corelib/symbol_test_03_multi',
   'corelib/symbol_test_none_multi',
   'corelib/uri_path_test',
   'corelib/uri_query_test',
+  'lib/async/async_await_sync_completer_test',
+  'lib/async/async_await_zones_test',
+  'lib/async/catch_errors2_test',
+  'lib/async/catch_errors3_test',
+  'lib/async/catch_errors_test',
+  'lib/async/future_microtask_test',
+  'lib/async/future_or_bad_type_test_00_multi',
+  'lib/async/future_or_bad_type_test_01_multi',
+  'lib/async/future_or_only_in_async_test_00_multi',
+  'lib/async/future_test_none_multi',
+  'lib/async/future_test_01_multi',
+  'lib/async/future_value_chain4_test',
+  'lib/async/print_test_01_multi',
+  'lib/async/print_test_none_multi',
+  'lib/async/slow_consumer3_test',
+  'lib/async/stream_controller_test',
+  'lib/async/stream_event_transformed_test',
+  'lib/async/stream_transformer_test',
+  'lib/async/zone_debug_test',
   'lib/convert/chunked_conversion1_test',
   'lib/math/min_max_test',
   'lib/typed_data/float32x4_test',
   'lib/typed_data/float64x2_functional_test',
   'lib/typed_data/int32x4_test',
   'lib/mirrors/abstract_class_test_00_multi',
   'lib/mirrors/abstract_test',
   'lib/mirrors/circular_factory_redirection_test_01_multi',
   'lib/mirrors/circular_factory_redirection_test_02_multi',
   'lib/mirrors/class_declarations_test_01_multi',
@@ skipping 309 matching lines @@
   'lib/html/mutationobserver_test',
   'lib/html/postmessage_structured_test',
   'lib/html/resource_http_test',
   'lib/html/transferables_test',
   'lib/html/webgl_1_test',
   'lib/html/wrapping_collections_test',
   // TODO(jmesserly): these are both under "dart:html" as well.
   'js_test',
   'js_util_test'
 ]);