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..6cece3736aa1f35d9b51811e5117f66ee1f20614 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 |overview_button_tray| locates on the right most position, no
+  // separator is required on its right side.

[tdanderson, 2017/02/16 20:25:03]

How about something like "Since OverviewButtonTray is located on the rightmost
position of a horizontal shelf, no separator is required." to make it more
general? Note that using the class name 'OverviewButtonTray' is preferred over
'|overview_button_tray|' since the |...| notation should only be used for
identifier names or |this|.

Also, in the SystemTray constructor above the set_separator_visibility() call
you say "Since |system_tray| locates on the right most position..." but this
isn't true if overview mode is enabled. The reason we don't need a separator for
the system tray is because the user avatar is on the right hand side and that is
sufficient to indicate separation. Can you also please change that documentation
accordingly?

[yiyix, 2017/02/16 20:43:43]

I have update all comments. Could you check it again? Thank you

+  set_separator_visibility(false);
+
   WmShell::Get()->AddShellObserver(this);
   WmShell::Get()->GetSessionStateDelegate()->AddSessionStateObserver(this);
 }