Perform type inference on constructor field initializer expressions.

pkg/front_end/testcases/inference/field_initializer_context_implicit.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;
+
+T f<T>() => null;
+
+class C implements B {
+  final /*@topType=int*/ x;
+  C() : x = /*@typeArgs=int*/ f();
+}
+
+abstract class B {
+  int get x;
+}
+
+main() {}