Set MethodInvocation.interfaceTarget during type inference.

pkg/front_end/testcases/inference/infer_conditional.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=num*/ a = 1 == 2 ? 1 : 2.0;
-var /*@topType=num*/ b = 1 == 2 ? 1.0 : 2;
+var /*@topType=num*/ a = 1 /*@target=Object::==*/ == 2 ? 1 : 2.0;
+var /*@topType=num*/ b = 1 /*@target=Object::==*/ == 2 ? 1.0 : 2;
 
 main() {
   a;
   b;
 }