fix #27259, implement covariance checking for strong mode and DDC

pkg/dev_compiler/lib/src/compiler/compiler.dart

Index: pkg/dev_compiler/lib/src/compiler/compiler.dart
diff --git a/pkg/dev_compiler/lib/src/compiler/compiler.dart b/pkg/dev_compiler/lib/src/compiler/compiler.dart
index 73f0914dfbf6e45c41c33d63f2808289e910428f..acef6c8993845b812fe73918a076864abbe937f7 100644
--- a/pkg/dev_compiler/lib/src/compiler/compiler.dart
+++ b/pkg/dev_compiler/lib/src/compiler/compiler.dart
@@ -267,18 +267,6 @@ class CompilerOptions {
   /// Whether to emit Closure Compiler-friendly code.
   final bool closure;
 
-  /// Hoist the types at instance creation sites.
-  final bool hoistInstanceCreation;
-
-  /// Hoist types from class signatures.
-  final bool hoistSignatureTypes;
-
-  /// Name types in type tests.
-  final bool nameTypeTests;
-
-  /// Hoist types in type tests.
-  final bool hoistTypeTests;
-
   /// Enable ES6 destructuring of named parameters. Off by default.
   ///
   /// Older V8 versions do not accept default values with destructuring in
@@ -314,10 +302,6 @@ class CompilerOptions {
       this.emitMetadata: false,
       this.closure: false,
       this.destructureNamedParams: false,
-      this.hoistInstanceCreation: true,
-      this.hoistSignatureTypes: false,
-      this.nameTypeTests: true,
-      this.hoistTypeTests: true,
       this.bazelMapping: const {},
       this.summaryOutPath});
 
@@ -332,10 +316,6 @@ class CompilerOptions {
         emitMetadata = args['emit-metadata'],
         closure = args['closure-experimental'],
         destructureNamedParams = args['destructure-named-params'],
-        hoistInstanceCreation = args['hoist-instance-creation'],
-        hoistSignatureTypes = args['hoist-signature-types'],
-        nameTypeTests = args['name-type-tests'],
-        hoistTypeTests = args['hoist-type-tests'],
         bazelMapping = _parseBazelMappings(args['bazel-mapping']),
         summaryOutPath = args['summary-out'];
 
@@ -372,18 +352,6 @@ class CompilerOptions {
               'allowing access to private members across library boundaries.',
           defaultsTo: false,
           hide: hide)
-      ..addFlag('hoist-instance-creation',
-          help: 'Hoist the class type from generic instance creations',
-          defaultsTo: true,
-          hide: hide)
-      ..addFlag('hoist-signature-types',
-          help: 'Hoist types from class signatures',
-          defaultsTo: false,
-          hide: hide)
-      ..addFlag('name-type-tests',
-          help: 'Name types used in type tests', defaultsTo: true, hide: hide)
-      ..addFlag('hoist-type-tests',
-          help: 'Hoist types used in type tests', defaultsTo: true, hide: hide)
       ..addOption('bazel-mapping',
           help:
               '--bazel-mapping=genfiles/to/library.dart,to/library.dart uses \n'