Introduce a type of View background that stays in sync with its host

ash/system/user/user_view.cc

Index: ash/system/user/user_view.cc
diff --git a/ash/system/user/user_view.cc b/ash/system/user/user_view.cc
index fe2ff061c8ceb920ba8c8d8fb6ab226e587c99ae..9fba39b240550d3d02aa99fcd4591beee87ccc13 100644
--- a/ash/system/user/user_view.cc
+++ b/ash/system/user/user_view.cc
@@ -81,8 +81,8 @@ views::View* CreateAddUserView(AddUserSessionPolicy policy,
                            kTrayPopupLabelHorizontalPadding + icon_padding);
   layout->set_minimum_cross_axis_size(kTrayPopupItemMinHeight);
   view->SetLayoutManager(layout);
-  view->set_background(
-      views::Background::CreateSolidBackground(kBackgroundColor));
+  view->set_background(views::Background::CreateThemedSolidBackground(
+      view, ui::NativeTheme::kColorId_BubbleBackground));
 
   int message_id = 0;
   switch (policy) {
@@ -364,13 +364,15 @@ void UserView::ToggleAddUserMenuOption() {
 
   views::View* container = new AddUserWidgetContents(
       base::Bind(&UserView::RemoveAddUserMenuOption, base::Unretained(this)));
+  views::View* add_user_view = CreateAddUserView(add_user_policy, this);
   container->SetBorder(views::CreatePaddedBorder(
-      views::CreateSolidSidedBorder(0, 0, 0, kSeparatorWidth, kBackgroundColor),
+      views::CreateSolidSidedBorder(0, 0, 0, kSeparatorWidth,
+                                    add_user_view->background()->get_color()),
       gfx::Insets(row_height, 0, 0, 0)));
   views::View* add_user_padding = new views::View();
-  add_user_padding->SetBorder(views::CreateSolidSidedBorder(
-      kMenuSeparatorVerticalPadding, 0, 0, 0, kBackgroundColor));
-  views::View* add_user_view = CreateAddUserView(add_user_policy, this);
+  add_user_padding->SetBorder(
+      views::CreateSolidSidedBorder(kMenuSeparatorVerticalPadding, 0, 0, 0,
+                                    add_user_view->background()->get_color()));
   add_user_padding->AddChildView(add_user_view);
   add_user_padding->SetLayoutManager(new views::FillLayout());
   container->AddChildView(add_user_padding);