fix fields that override getters/setters

test/codegen/expect/fieldtest.js

 var fieldtest;
 (function(exports) {
   'use strict';
   class A extends core.Object {
     A() {
       this.x = 42;
     }
   }
   let B$ = dart.generic(function(T) {
     class B extends core.Object {
@@ skipping 34 matching lines @@
     get q() {
       return 'life, ' + 'the universe ' + 'and everything';
     },
     get z() {
       return 42;
     },
     set z(value) {
       exports.y = dart.as(value, core.int);
     }
   });
+  class BaseWithGetter extends core.Object {
+    get foo() {
+      return 1;
+    }
+  }
+  class Derived extends BaseWithGetter {
+    Derived() {
+      this.foo = 2;
+      this.bar = 3;
+      super.BaseWithGetter();
+    }
+  }
+  dart.virtualField(Derived, 'foo');
   // Function main: () → void
   function main() {
     let a = new A();
     foo(a);
     bar(a);
     core.print(baz(a));
   }
   // Exports:
   exports.A = A;
   exports.B$ = B$;
   exports.B = B;
   exports.foo = foo;
   exports.bar = bar;
   exports.baz = baz;
   exports.compute = compute;
+  exports.BaseWithGetter = BaseWithGetter;
+  exports.Derived = Derived;
   exports.main = main;
 })(fieldtest || (fieldtest = {}));