Lift nearly all top-level type inference restrictions.

pkg/front_end/testcases/inference/inferred_type_cascade.dart

 // Copyright (c) 2017, 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.
 
 /*@testedFeatures=inference*/
 library test;
 
 class A {
   int a;
   List<int> b;
   void m() {}
 }
 
 var /*@topType=A*/ v = new A()
   .. /*@target=A::a*/ a = 1
   .. /*@target=A::b*/ b. /*@target=List::add*/ add(2)
   .. /*@target=A::m*/ m();
+
+main() {}