Fix type inference of getters that "override" setters and vice versa.

pkg/front_end/testcases/inference/infer_setter_cross_to_getter.dart

Index: pkg/front_end/testcases/inference/infer_setter_cross_to_getter.dart
diff --git a/pkg/front_end/testcases/inference/infer_setter_cross_to_getter.dart b/pkg/front_end/testcases/inference/infer_setter_cross_to_getter.dart
new file mode 100644
index 0000000000000000000000000000000000000000..47f35d5de8780ebe4bd22a0233f4f12ac55b0333
--- /dev/null
+++ b/pkg/front_end/testcases/inference/infer_setter_cross_to_getter.dart
@@ -0,0 +1,16 @@
+// 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;
+
+abstract class A {
+  double get x;
+}
+
+abstract class B extends A {
+  void set x(/*@topType=double*/ value);
+}
+
+main() {}