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 27609771d7d4feceac7ad6445c193a27aa089627..12e20f3a137dbbf9000a352f5b1952e760dc46ee 100644
--- a/ash/common/system/tray/system_tray.cc
+++ b/ash/common/system/tray/system_tray.cc
@@ -221,6 +221,10 @@ 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);
   }