fix #26393, treat tear offs as definite functions

pkg/analyzer/lib/src/task/strong/checker.dart

Index: pkg/analyzer/lib/src/task/strong/checker.dart
diff --git a/pkg/analyzer/lib/src/task/strong/checker.dart b/pkg/analyzer/lib/src/task/strong/checker.dart
index b20d702e71f4f1c4fa53b9c4974e48b22260857e..8b21d95a2b41217eaf79f90c223b0bdc87948988 100644
--- a/pkg/analyzer/lib/src/task/strong/checker.dart
+++ b/pkg/analyzer/lib/src/task/strong/checker.dart
@@ -21,7 +21,7 @@ import 'package:analyzer/src/generated/type_system.dart';
 
 import 'ast_properties.dart';
 
-bool isKnownFunction(Expression expression, {bool instanceMethods: false}) {
+bool isKnownFunction(Expression expression) {
   Element element = null;
   if (expression is ParenthesizedExpression) {
     expression = (expression as ParenthesizedExpression).expression;
@@ -36,7 +36,7 @@ bool isKnownFunction(Expression expression, {bool instanceMethods: false}) {
   // First class functions and static methods, where we know the original
   // declaration, will have an exact type, so we know a downcast will fail.
   return element is FunctionElement ||
-      element is MethodElement && (instanceMethods || element.isStatic);
+      element is MethodElement;
 }
 
 DartType _elementType(Element e) {
@@ -1004,7 +1004,7 @@ class CodeChecker extends RecursiveAstVisitor {
     // a dynamic parameter type requires a dynamic call in general.
     // However, as an optimization, if we have an original definition, we know
     // dynamic is reified as Object - in this case a regular call is fine.
-    if (isKnownFunction(call, instanceMethods: true)) {
+    if (isKnownFunction(call)) {
       return false;
     }
     return rules.anyParameterType(ft, (pt) => pt.isDynamic);