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

pkg/front_end/lib/src/fasta/kernel/kernel_class_builder.dart

 // Copyright (c) 2016, 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.
 
 library fasta.kernel_class_builder;
 
 import 'package:front_end/src/fasta/kernel/kernel_shadow_ast.dart'
     show KernelMember;
 
 import 'package:kernel/ast.dart'
@@ skipping 164 matching lines @@
       return new DillMemberBuilder(field, this);
     });
     Field field = constructorsField.target;
     ListLiteral literal = field.initializer;
     literal.expressions
         .add(new StaticGet(constructor.target)..parent = literal);
   }
 
   void checkOverrides(ClassHierarchy hierarchy) {
     hierarchy.forEachOverridePair(cls, checkOverride);
+    hierarchy.forEachCrossOverridePair(cls, handleCrossOverride);
   }
 
   void checkOverride(
       Member declaredMember, Member interfaceMember, bool isSetter) {
     if (declaredMember is Constructor || interfaceMember is Constructor) {
       internalError(
           "Constructor in override check.", fileUri, declaredMember.fileOffset);
     }
     if (declaredMember is Procedure && interfaceMember is Procedure) {
       if (declaredMember.kind == ProcedureKind.Method &&
           interfaceMember.kind == ProcedureKind.Method) {
         checkMethodOverride(declaredMember, interfaceMember);
         return;
       }
     }
     // TODO(ahe): Handle other cases: accessors, operators, and fields.
 
     // Also record any cases where a field or getter/setter overrides something
     // in a superclass, since this information will be needed for type
     // inference.
     if (declaredMember is KernelMember &&
         identical(declaredMember.enclosingClass, cls)) {
       KernelMember.recordOverride(declaredMember, interfaceMember);
     }
   }
 
+  void handleCrossOverride(
+      Member declaredMember, Member interfaceMember, bool isSetter) {
+    // Record any cases where a field or getter/setter has a corresponding (but
+    // opposite) getter/setter in a superclass, since this information will be
+    // needed for type inference.
+    if (declaredMember is KernelMember &&
+        identical(declaredMember.enclosingClass, cls)) {
+      KernelMember.recordCrossOverride(declaredMember, interfaceMember);
+    }
+  }
+
   void checkMethodOverride(
       Procedure declaredMember, Procedure interfaceMember) {
     if (declaredMember.enclosingClass != cls) {
       // TODO(ahe): Include these checks as well, but the message needs to
       // explain that [declaredMember] is inherited.
       return;
     }
     assert(declaredMember.kind == ProcedureKind.Method);
     assert(interfaceMember.kind == ProcedureKind.Method);
     FunctionNode declaredFunction = declaredMember.function;
@@ skipping 61 matching lines @@
       }
     }
   }
 
   String get fullNameForErrors {
     return isMixinApplication
         ? "${supertype.fullNameForErrors} with ${mixedInType.fullNameForErrors}"
         : name;
   }
 }