[ash-md] Adjusts layout of lists with sticky header rows to match specs

ash/common/system/tray/tray_popup_utils.cc

Index: ash/common/system/tray/tray_popup_utils.cc
diff --git a/ash/common/system/tray/tray_popup_utils.cc b/ash/common/system/tray/tray_popup_utils.cc
index a7cda5a74fec0bd57c525c16bb061856ee7a0b44..df01354414b4b84791d18e9981c1aef74e6795d5 100644
--- a/ash/common/system/tray/tray_popup_utils.cc
+++ b/ash/common/system/tray/tray_popup_utils.cc
@@ -427,6 +427,16 @@ views::Separator* TrayPopupUtils::CreateListItemSeparator(bool left_inset) {
   return separator;
 }
 
+views::Separator* TrayPopupUtils::CreateListHeaderSeparator() {
+  views::Separator* separator =
+      new views::Separator(views::Separator::HORIZONTAL);
+  separator->SetColor(kHorizontalSeparatorColor);
+  separator->SetPreferredSize(kSeparatorWidth);
+  separator->SetBorder(views::CreateEmptyBorder(
+      kMenuSeparatorVerticalPadding - kSeparatorWidth, 0, 0, 0));
+  return separator;
+}
+
 bool TrayPopupUtils::CanOpenWebUISettings(LoginStatus status) {
   // TODO(tdanderson): Consider moving this into WmShell, or introduce a
   // CanShowSettings() method in each delegate type that has a