Hook up full list literal type inference logic.

pkg/front_end/testcases/inference/list_literals_top_level.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;
 
 var /*@topType=List<int>*/ x1 = /*@typeArgs=int*/ [1, 2, 3];
 test1() {
   x1.add(/*error:ARGUMENT_TYPE_NOT_ASSIGNABLE*/ 'hi');
   x1.add(/*error:ARGUMENT_TYPE_NOT_ASSIGNABLE*/ 4.0);
   x1.add(4);
   List<num> y = x1;
 }
 
 var /*@topType=List<num>*/ x2 = /*@typeArgs=num*/ [1, 2.0, 3];
 test2() {
   x2.add(/*error:ARGUMENT_TYPE_NOT_ASSIGNABLE*/ 'hi');
   x2.add(4.0);
   List<int> y = /*info:ASSIGNMENT_CAST*/ x2;
 }
+
+main() {
+  test1();
+  test2();
+}