fix #28630, instance method tear-offs are treated as strict arrows

pkg/analyzer/lib/src/generated/error_verifier.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.src.generated.error_verifier;
 
 import 'dart:collection';
 import "dart:math" as math;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 15 matching lines @@
 import 'package:analyzer/src/generated/element_resolver.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/java_engine.dart';
 import 'package:analyzer/src/generated/parser.dart' show ParserErrorCode;
 import 'package:analyzer/src/generated/resolver.dart';
 import 'package:analyzer/src/generated/sdk.dart' show DartSdk, SdkLibrary;
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/generated/utilities_dart.dart';
 import 'package:analyzer/src/task/dart.dart';
 import 'package:analyzer/src/task/strong/checker.dart' as checker
-    show isKnownFunction;
+    show hasStrictArrow;
 
 /**
  * A visitor used to traverse an AST structure looking for additional errors and
  * warnings not covered by the parser and resolver.
  */
 class ErrorVerifier extends RecursiveAstVisitor<Object> {
   /**
    * Static final string with value `"getter "` used in the construction of the
    * [StaticWarningCode.NON_ABSTRACT_CLASS_INHERITS_ABSTRACT_MEMBER_ONE], and
    * similar, error code messages.
@@ skipping 6194 matching lines @@
     DartType staticReturnType = getStaticType(returnExpression);
     if (staticReturnType != null && _enclosingFunction.isAsynchronous) {
       return _typeProvider.futureType.instantiate(
           <DartType>[staticReturnType.flattenFutures(_typeSystem)]);
     }
     return staticReturnType;
   }
 
   bool _expressionIsAssignableAtType(Expression expression,
       DartType actualStaticType, DartType expectedStaticType) {
-    bool concrete = _options.strongMode && checker.isKnownFunction(expression);
+    bool concrete = _options.strongMode && checker.hasStrictArrow(expression);
     if (concrete && actualStaticType is FunctionType) {
       actualStaticType =
           _typeSystem.functionTypeToConcreteType(actualStaticType);
       // TODO(leafp): Move the Downcast functionality here.
     }
     return _typeSystem.isAssignableTo(actualStaticType, expectedStaticType);
   }
 
   MethodElement _findOverriddenMemberThatMustCallSuper(MethodDeclaration node) {
     ExecutableElement overriddenMember = _getOverriddenMember(node.element);
@@ skipping 815 matching lines @@
 class _InvocationCollector extends RecursiveAstVisitor {
   final List<String> superCalls = <String>[];
 
   @override
   visitMethodInvocation(MethodInvocation node) {
     if (node.target is SuperExpression) {
       superCalls.add(node.methodName.name);
     }
   }
 }