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

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 1260 matching lines @@
   void set _typeInferrer(KernelTypeInferrer value);
 
   void setInferredType(
       TypeInferenceEngineImpl engine, String uri, DartType inferredType);
 
   static FieldNode getFieldNode(Member member) {
     if (member is KernelMember) return member._fieldNode;
     return null;
   }
 
+  static void recordCrossOverride(
+      KernelMember member, Member overriddenMember) {
+    if (member._fieldNode != null) {
+      member._fieldNode.crossOverrides.add(overriddenMember);
+    }
+  }
+
   static void recordOverride(KernelMember member, Member overriddenMember) {
     if (member._fieldNode != null) {
       member._fieldNode.overrides.add(overriddenMember);
     }
   }
 }
 
 /// Shadow object for [MethodInvocation].
 class KernelMethodInvocation extends MethodInvocation
     implements KernelExpression {
@@ skipping 930 matching lines @@
   }
 
   transformChildren(v) {
     return internalError("Internal error: Unsupported operation.");
   }
 
   visitChildren(v) {
     return internalError("Internal error: Unsupported operation.");
   }
 }