fix #27643, failed to virtualize fields if an abstract one is mixed in

R=vsm@google.com

Review URL: https://codereview.chromium.org/2441693003 .

pkg/dev_compiler/lib/src/compiler/js_field_storage.dart

@@ -30,10 +30,6 @@ PropertyOverrideResult checkForPropertyOverride(
     var setter = superprop.setter;
     bool hasSetter = setter != null && !setter.isAbstract;
     if (hasSetter) foundSetter = true;
-
-    // Stop if this is an abstract getter/setter
-    // TODO(jmesserly): why were we doing this?
-    if (!hasGetter && !hasSetter) break;
   }
 
   return new PropertyOverrideResult(foundGetter, foundSetter);

pkg/dev_compiler/test/codegen/language/mixin_abstract_getter_test.dart

@@ -0,0 +1,43 @@
+// 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.
+
+import 'package:expect/expect.dart';
+
+abstract class B {
+  int get x;
+}
+
+class C {
+  int get x => 42;
+}
+
+class D extends C with B {
+  final int x;
+
+  D(this.x);
+}
+
+
+class C2 {
+  int get x => 42;
+}
+
+abstract class B2 extends C2 {
+  int get x;
+}
+
+class D2 extends B2 {
+  final int x;
+
+  D2(this.x);
+}
+
+
+void main() {
+  var d = new D(17);
+  Expect.equals(d.x, 17);
+
+  var d2 = new D2(17);
+  Expect.equals(d.x, 17);
+}

pkg/dev_compiler/test/codegen/lib/math/implement_rectangle_test.dart

@@ -1,3 +1,7 @@
+// 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.
+
 import 'dart:math' hide Rectangle;
 import 'dart:math' as math show Point, Rectangle, MutableRectangle;
 import 'package:expect/expect.dart' show Expect;