Chrome OS: adjust wifi icons.

Chrome OS: adjust wifi icons.

1. In the system tray, if wifi is disabled, the icon is a white wedge
   with strikethrough. If wifi is enabled and no network is connected,
   the icon is an empty wedge without a strikethrough.
2. In the default view (system bubble row) the icon is either a normal,
   badged icon if connected, an empty wedge if enabled but disconnected,
   or a full strength wedge with strikethough but with 0.54a if disabled.
3. In the notification, the icon is full strength with or without
   strikethough, depending on enabled state.

BUG=711555
Review-Url: https://codereview.chromium.org/2817223003
Cr-Commit-Position: refs/heads/master@{#464999}
(cherry picked from commit 7735ed2d044b9afaa1c853f003084a55e6c6e42a)