Implement override-based inference of instance fields.

pkg/front_end/testcases/inference/infer_field_override_with_substitution.dart.strong.expect

Index: pkg/front_end/testcases/inference/infer_field_override_with_substitution.dart.strong.expect
diff --git a/pkg/front_end/testcases/inference/infer_field_override_with_substitution.dart.strong.expect b/pkg/front_end/testcases/inference/infer_field_override_with_substitution.dart.strong.expect
new file mode 100644
index 0000000000000000000000000000000000000000..8a200d7d40d99d930399cdd7307fa71ae0a33a96
--- /dev/null
+++ b/pkg/front_end/testcases/inference/infer_field_override_with_substitution.dart.strong.expect
@@ -0,0 +1,21 @@
+library test;
+import self as self;
+import "dart:core" as core;
+
+abstract class A<T extends core::Object> extends core::Object {
+  field core::List<self::A::T> z = null;
+  constructor •() → void
+    : super core::Object::•()
+    ;
+  abstract get x() → core::List<self::A::T>;
+  abstract set y(core::List<self::A::T> value) → void;
+}
+class B extends self::A<core::int> {
+  field core::List<core::int> x = null;
+  field core::List<core::int> y = null;
+  field core::List<core::int> z = null;
+  constructor •() → void
+    : super self::A::•()
+    ;
+}
+static method main() → dynamic {}