fix #26393, treat tear offs as definite functions

pkg/analyzer/test/src/task/strong/checker_test.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.
 
 library analyzer.test.src.task.strong.checker_test;
 
 import '../../../reflective_tests.dart';
 import 'strong_test_helper.dart';
 
 void main() {
@@ skipping 1388 matching lines @@
   C c = new C();
   {
     Function2<B, A> f;
     f = c.top;
     f = c.left;
     f = c.right;
     f = c.bot;
   }
   {
     Function2<B, B> f;
-    f = /*warning:DOWN_CAST_COMPOSITE*/c.top;
+    f = /*error:STATIC_TYPE_ERROR*/c.top;

[Leaf, 2016/08/05 23:33:05]

This doesn't feel right.  I think this is the "stupid cast" logic coming into
play?  But this cast could succeed: `c` could contain a subclass of C which
overrides top with the right type (since it is a subtype).  Assuming this is
right about where this comes from, then I think the cast logic that inserts this
error shouldn't do so for methods (since they can be overridden).

     f = c.left;
-    f = /*warning:DOWN_CAST_COMPOSITE*/c.right;
+    f = /*error:STATIC_TYPE_ERROR*/c.right;
     f = c.bot;
   }
   {
     Function2<A, A> f;
-    f = /*warning:DOWN_CAST_COMPOSITE*/c.top;
-    f = /*warning:DOWN_CAST_COMPOSITE*/c.left;
+    f = /*error:STATIC_TYPE_ERROR*/c.top;
+    f = /*error:STATIC_TYPE_ERROR*/c.left;
     f = c.right;
     f = c.bot;
   }
   {
     Function2<A, B> f;
-    f = /*warning:DOWN_CAST_COMPOSITE*/c.top;
-    f = /*warning:DOWN_CAST_COMPOSITE*/c.left;
-    f = /*warning:DOWN_CAST_COMPOSITE*/c.right;
+    f = /*error:STATIC_TYPE_ERROR*/c.top;
+    f = /*error:STATIC_TYPE_ERROR*/c.left;
+    f = /*error:STATIC_TYPE_ERROR*/c.right;
     f = c.bot;
   }
 }
 ''');
   }
 
   void test_functionTypingAndSubtyping_intAndObject() {
     checkFile('''
 typedef Object Top(int x);      // Top of the lattice
 typedef int Left(int x);        // Left branch
@@ skipping 2212 matching lines @@
     // Regression test for https://github.com/dart-lang/sdk/issues/25069
     checkFile('''
 typedef int Foo();
 void foo() {}
 void main () {
   Foo x = /*error:INVALID_ASSIGNMENT,info:USE_OF_VOID_RESULT*/foo();
 }
 ''');
   }
 }