Remove the extra separator appears beside overview tray

ash/common/system/overview/overview_button_tray.cc

Index: ash/common/system/overview/overview_button_tray.cc
diff --git a/ash/common/system/overview/overview_button_tray.cc b/ash/common/system/overview/overview_button_tray.cc
index 4bd5aadfc1498c4b4ca1f3de65ed91a1f4d23046..105320ed90168faa07bfc8e2e0f57cf75f55bc2e 100644
--- a/ash/common/system/overview/overview_button_tray.cc
+++ b/ash/common/system/overview/overview_button_tray.cc
@@ -56,6 +56,10 @@ OverviewButtonTray::OverviewButtonTray(WmShelf* wm_shelf)
   SetIconBorderForShelfAlignment();
   tray_container()->AddChildView(icon_);
 
+  // Since OverviewButtonTray is located on the rightmost position of a
+  // horizontal shelf, no separator is required.
+  set_separator_visibility(false);
+
   WmShell::Get()->AddShellObserver(this);
   WmShell::Get()->GetSessionStateDelegate()->AddSessionStateObserver(this);
 }