Implement override-based inference of instance fields.

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 KernelField;
+
 import 'package:kernel/ast.dart'
     show
         Class,
         Constructor,
         DartType,
         Expression,
         Field,
         FunctionNode,
         InterfaceType,
         ListLiteral,
@@ skipping 171 matching lines @@
           "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 overrides something in a superclass,
+    // since this information will be needed for type inference.
+    if (declaredMember is KernelField &&
+        identical(declaredMember.enclosingClass, cls)) {
+      KernelField.recordOverride(declaredMember, interfaceMember, isSetter);
+    }
   }
 
   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);
@@ skipping 63 matching lines @@
       }
     }
   }
 
   String get fullNameForErrors {
     return isMixinApplication
         ? "${supertype.fullNameForErrors} with ${mixedInType.fullNameForErrors}"
         : name;
   }
 }