Add dart:io stubs to ddc sdk, define dart.library.html

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 2143 matching lines @@
   'lib/mirrors/library_exports_shown_test',
   'lib/mirrors/library_import_deferred_loading_test',
   'lib/mirrors/library_imports_bad_metadata_test_01_multi',
   'lib/mirrors/library_imports_deferred_test',
   'lib/mirrors/library_imports_hidden_test',
   'lib/mirrors/library_imports_metadata_test',
   'lib/mirrors/library_imports_prefixed_show_hide_test',
   'lib/mirrors/library_imports_prefixed_test',
   'lib/mirrors/library_imports_shown_test',
   'lib/mirrors/library_metadata2_test_01_multi',
-  'lib/mirrors/library_uri_io_test',
   'lib/mirrors/load_library_test',
   'lib/mirrors/metadata_allowed_values_test_01_multi',
   'lib/mirrors/metadata_allowed_values_test_02_multi',
   'lib/mirrors/metadata_allowed_values_test_03_multi',
   'lib/mirrors/metadata_allowed_values_test_04_multi',
   'lib/mirrors/metadata_allowed_values_test_05_multi',
   'lib/mirrors/metadata_allowed_values_test_06_multi',
   'lib/mirrors/metadata_allowed_values_test_07_multi',
   'lib/mirrors/metadata_allowed_values_test_08_multi',
   'lib/mirrors/metadata_allowed_values_test_09_multi',
@@ skipping 247 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'
 ]);