Refactor material list styles

PiperOrigin-RevId: 259973461

Author: Googler

angular_components/lib/material_list/_size.scss renamed to angular_components/lib/material_list/_common_constants.scss

@@ -0,0 +1,8 @@
+// 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:angular_components/material_list/_common_constants';
+@import 'package:angular_components/css/material/material';
+
+$list-item-button-hover-background: $mat-grey-200;

angular_components/lib/material_list/_constants.scss

@@ -2,7 +2,7 @@
 // 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 'size';
+@import 'package:angular_components/material_list/constants';
 @import 'package:angular_components/css/material/material';
 
 @mixin list-item-base {
@@ -61,7 +61,7 @@
     &:hover,
     &:focus,
     &.active {
-      background: $mat-grey-200;
+      background: $list-item-button-hover-background;
     }
 
     &.disabled {