Closures shouldn't have fuzzy arrow type.

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

 // Copyright (c) 2015, 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.
 
 /// Defines static information collected by the type checker and used later by
 /// emitters to generate code.
 // TODO(jmesserly): this was ported from package:dev_compiler, and needs to be
 // refactored to fit into analyzer.
 library analyzer.src.task.strong.info;
 
@@ skipping 500 matching lines @@
     var source = (node.root as CompilationUnit).element.source;
     return new AnalysisError(source, begin, length, toErrorCode(), arguments);
   }
 
   // TODO(jmesserly): review the usage of error codes. We probably want our own,
   // as well as some DDC specific [ErrorType]s.
   ErrorCode toErrorCode();
 
   static bool isKnownFunction(Expression expression) {
     Element element = null;
-    if (expression is PropertyAccess) {
+    if (expression is FunctionExpression) {
+      return true;
+    } else if (expression is PropertyAccess) {
       element = expression.propertyName.staticElement;
     } else if (expression is Identifier) {
       element = expression.staticElement;
     }
     // 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 && element.isStatic;
   }
 }
 
 class StaticTypeError extends StaticError {
   final DartType baseType;
   final DartType expectedType;
 
   StaticTypeError(TypeSystem rules, Expression expression, this.expectedType)
       : baseType = expression.staticType ?? DynamicTypeImpl.instance,
         super(expression);
 
   @override
   List<Object> get arguments => [node, baseType, expectedType];
   @override
   String get message => 'Type check failed: {0} ({1}) is not of type {2}';
 
   @override
   String get name => 'STRONG_MODE_STATIC_TYPE_ERROR';
 }