Update chromeos system menu buttons for MD.

ash/common/system/tray/tray_utils.h

Index: ash/common/system/tray/tray_utils.h
diff --git a/ash/common/system/tray/tray_utils.h b/ash/common/system/tray/tray_utils.h
index beb89876031cebef18f24d76dc02550ea0dcab54..b74116913267b26b3d4ddcc5a0bb6a4f8d121d98 100644
--- a/ash/common/system/tray/tray_utils.h
+++ b/ash/common/system/tray/tray_utils.h
@@ -12,7 +12,9 @@
 #include "base/strings/string16.h"
 
 namespace views {
+class ButtonListener;
 class Label;
+class LabelButton;
 class Separator;
 class View;
 }
@@ -21,6 +23,17 @@ namespace ash {
 
 class TrayItemView;
 
+// Creates a button for use in the system menu that has no visible border when

[tdanderson, 2016/11/01 22:38:50]

nit: please add a comment that the caller assumes ownership of the returned
button (here and for CreateTrayPopupButton())

[Evan Stade, 2016/11/01 23:54:09]

I have a hard time seeing how one would reasonably conclude otherwise... but
done.

+// not being hovered/clicked.

[tdanderson, 2016/11/01 22:38:50]

nit: consider eliminating the double negative in the documentation such as "only
has a visible border when hovered/clicked"

[Evan Stade, 2016/11/01 23:54:09]

Done.

+views::LabelButton* CreateTrayPopupBorderlessButton(
+    views::ButtonListener* listener,
+    const base::string16& text);
+
+// Creates a button for use in the system menu. For non-MD, this does the same

[tdanderson, 2016/11/01 22:38:50]

nit: please give a bit more description about what happens for MD (i.e.,
"creates a material design text button" and list any visual properties)

[Evan Stade, 2016/11/01 23:54:09]

Done.

+// thing as the above.
+views::LabelButton* CreateTrayPopupButton(views::ButtonListener* listener,
+                                          const base::string16& text);
+
 // Sets up a Label properly for the tray (sets color, font etc.).
 void SetupLabelForTray(views::Label* label);