Start cleaning up the HTML tests.

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 2409 matching lines @@
   'corelib/regexp/standalones_test',
   'corelib/string_from_environment2_test',
   'corelib/string_from_environment_test',
   'corelib/string_from_list_test',
   'lib/convert/chunked_conversion_json_encode1_test',
   'lib/convert/chunked_conversion_utf84_test',
   'lib/convert/chunked_conversion_utf88_test',
   'lib/convert/chunked_conversion_utf8_test',
   'lib/convert/line_splitter_test',
   'lib/html/cross_frame_test',
-  'lib/html/css_rule_list_test',
-  'lib/html/custom/constructor_calls_created_synchronously_test',
-  'lib/html/custom/created_callback_test',
-  'lib/html/custom/document_register_basic_test',
-  'lib/html/custom/document_register_type_extensions_test',
-  'lib/html/custom/element_upgrade_test',
-  'lib/html/custom_elements_23127_test',
-  'lib/html/custom_elements_test',
-  'lib/html/datalistelement_test',
-  'lib/html/documentfragment_test',
-  'lib/html/element_add_test',
-  'lib/html/element_classes_test',
   'lib/html/element_test',
   'lib/html/events_test',
   'lib/html/fileapi_test',
   'lib/html/filereader_test',
   'lib/html/fontface_loaded_test',
-  'lib/html/htmlcollection_test',
-  'lib/html/htmlelement_test',
-  'lib/html/htmloptionscollection_test',
-  'lib/html/indexeddb_2_test',
   'lib/html/js_function_getter_trust_types_test',
-  'lib/html/js_test',
-  'lib/html/js_util_test',
   'lib/html/js_typed_interop_side_cast_exp_test',
   'lib/html/js_typed_interop_side_cast_test',
   'lib/html/keyboard_event_test',
   'lib/html/localstorage_test',
   'lib/html/mutationobserver_test',
   'lib/html/node_test',
   'lib/html/node_validator_important_if_you_suppress_make_the_bug_critical_test',
   'lib/html/postmessage_structured_test',
   'lib/html/queryall_test',
   'lib/html/resource_http_test',
   'lib/html/selectelement_test',
   'lib/html/track_element_constructor_test',
   'lib/html/transferables_test',
   'lib/html/typed_arrays_range_checks_test',
   'lib/html/typing_test',
   'lib/html/unknownelement_test',
   'lib/html/webgl_1_test',
   'lib/html/window_nosuchmethod_test',
   'lib/html/wrapping_collections_test',
   // TODO(jmesserly): these are both under "dart:html" as well.
   'js_test',
   'js_util_test'
 ]);