Implement type inference of method invocations in Fasta.

pkg/front_end/testcases/inference/infer_prefix_expression_custom.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 {
   A();
   int operator ~() => 1;
   double operator -() => 2.0;
 }
 
 var /*@topType=A*/ a = new A();
 var /*@topType=int*/ v_complement = ~a;
 var /*@topType=double*/ v_negate = -a;
+
+main() {
+  a;
+  v_complement;
+  v_negate;
+}