Implement override-based inference of instance fields.

pkg/front_end/testcases/inference_new/field_inference_circularity.dart.strong.expect

Index: pkg/front_end/testcases/inference_new/field_inference_circularity.dart.strong.expect
diff --git a/pkg/front_end/testcases/inference_new/field_inference_circularity.dart.strong.expect b/pkg/front_end/testcases/inference_new/field_inference_circularity.dart.strong.expect
new file mode 100644
index 0000000000000000000000000000000000000000..9454b582c13ba5c801a0aeae4c324fa00757056d
--- /dev/null
+++ b/pkg/front_end/testcases/inference_new/field_inference_circularity.dart.strong.expect
@@ -0,0 +1,19 @@
+library test;
+import self as self;
+import "dart:core" as core;
+
+class A extends core::Object {
+  field dynamic x = () → dynamic => new self::B::•().{self::B::x};
+  field () → dynamic y = () → dynamic => new self::B::•().{self::B::x};
+  constructor •() → void
+    : super core::Object::•()
+    ;
+}
+class B extends self::A {
+  field dynamic x = null;
+  field () → dynamic y = null;
+  constructor •() → void
+    : super self::A::•()
+    ;
+}
+static method main() → dynamic {}