Remove the extra separator appears on the right side of the shelf

ash/common/system/tray/system_tray.cc

Index: ash/common/system/tray/system_tray.cc
diff --git a/ash/common/system/tray/system_tray.cc b/ash/common/system/tray/system_tray.cc
index cb725a9d4b6603c4ed781c986ee97dd0e596ddcb..625f19578e6914fbbed28ba7442b9746e2bbfe08 100644
--- a/ash/common/system/tray/system_tray.cc
+++ b/ash/common/system/tray/system_tray.cc
@@ -224,6 +224,10 @@ SystemTray::SystemTray(WmShelf* wm_shelf)
   if (MaterialDesignController::IsShelfMaterial()) {
     SetInkDropMode(InkDropMode::ON);
     SetContentsBackground(false);
+
+    // Since |system_tray| locates on the right most position, no separator is
+    // required on its right side.
+    set_separator_visibility(false);
   } else {
     SetContentsBackground(true);
   }