dark_mode: Toast is dark themed by default.

Bug: 1145255
Change-Id: I20b9a1352209948897d8174786a58122c3f5a37b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2518322Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Min Chen <minch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823676}

ash/system/toast/toast_overlay.cc

@@ -12,7 +12,6 @@
 #include "ash/shell.h"
 #include "ash/strings/grit/ash_strings.h"
 #include "ash/style/ash_color_provider.h"
-#include "ash/style/scoped_light_mode_as_default.h"
 #include "ash/wm/work_area_insets.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
@@ -84,7 +83,6 @@ class ToastOverlayLabel : public views::Label {
   // views::Label:
   void OnThemeChanged() override {
     views::Label::OnThemeChanged();
-    ScopedLightModeAsDefault scoped_light_mode_as_default;
     SetEnabledColor(AshColorProvider::Get()->GetContentLayerColor(
         AshColorProvider::ContentLayerType::kTextColorPrimary));
   }
@@ -152,7 +150,6 @@ class ToastOverlayButton : public views::LabelButton {
   // views::LabelButton:
   void OnThemeChanged() override {
     views::LabelButton::OnThemeChanged();
-    ScopedLightModeAsDefault scoped_light_mode_as_default;
     const auto* color_provider = AshColorProvider::Get();
     SetInkDropBaseColor(color_provider->GetRippleAttributes().base_color);
     SetEnabledTextColors(color_provider->GetContentLayerColor(
@@ -229,7 +226,6 @@ class ToastOverlayView : public views::View {
 
   void OnThemeChanged() override {
     views::View::OnThemeChanged();
-    ScopedLightModeAsDefault scoped_light_mode_as_default;
     auto* color_provider = AshColorProvider::Get();
     SetBackground(
         views::CreateSolidBackground(color_provider->GetBaseLayerColor(