Implement override-based type inference for instance methods.

pkg/front_end/testcases/inference/circular_method_inference.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;
+
+// The following code is illegal because it has a loop in the class hierarchy.
+// We need to make sure that the compiler doesn't try to error recover in a way
+// that causes type inference for the method `f` to go into an infinite loop.
+
+abstract class A extends B {
+  /*@topType=dynamic*/ f(/*@topType=dynamic*/ x);
+}
+
+abstract class B extends A {
+  /*@topType=dynamic*/ f(/*@topType=dynamic*/ x);
+}
+
+main() {}