Implement override-based inference of instance fields.

pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.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.
 
 /// This file declares a "shadow hierarchy" of concrete classes which extend
 /// the kernel class hierarchy, adding methods and fields needed by the
 /// BodyBuilder.
 ///
 /// Instances of these classes may be created using the factory methods in
 /// `ast_factory.dart`.
@@ skipping 672 matching lines @@
   }
 }
 
 /// Concrete shadow object representing a field in kernel form.
 class KernelField extends Field {
   FieldNode _fieldNode;
 
   KernelTypeInferrer _typeInferrer;
 
   KernelField(Name name, {String fileUri}) : super(name, fileUri: fileUri) {}
+
+  static FieldNode getFieldNode(Field field) {
+    if (field is KernelField) return field._fieldNode;
+    return null;
+  }
+
+  static void recordOverride(
+      KernelField field, Member overriddenMember, bool isSetter) {
+    if (field._fieldNode != null) {
+      if (isSetter && overriddenMember is Field) {
+        // When overriding a field, we are called twice; once for the setter and
+        // once for the getter.  Ignore the setter.
+        return;
+      }
+      field._fieldNode.overrides.add(overriddenMember);
+    }
+  }
 }
 
 /// Concrete shadow object representing a for-in loop in kernel form.
 class KernelForInStatement extends ForInStatement implements KernelStatement {
   final bool _declaresVariable;
 
   KernelForInStatement(VariableDeclaration variable, Expression iterable,
       Statement body, this._declaresVariable,
       {bool isAsync: false})
       : super(variable, iterable, body, isAsync: isAsync);
@@ skipping 1584 matching lines @@
   }
 
   transformChildren(v) {
     return internalError("Internal error: Unsupported operation.");
   }
 
   visitChildren(v) {
     return internalError("Internal error: Unsupported operation.");
   }
 }