Use non-deprecated color function for Exit Session background color.

Intended change:
Light mode: kGoogleRed700 -> kGoogleRed600
Dark mode: kGoogleRed700 -> kGoogleRed300

Bug: 1028245
Change-Id: Ida204c593a21f018fb39adc9091653012c1b259d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1933943
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Stefan Kuhne <skuhne@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Commit-Queue: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#718974}

diff --git a/ash/system/session/logout_button_tray.cc b/ash/system/session/logout_button_tray.cc
index 5e0e654..92e592b 100644
--- a/ash/system/session/logout_button_tray.cc
+++ b/ash/system/session/logout_button_tray.cc

@@ -13,7 +13,6 @@
 #include "ash/shelf/shelf.h"
 #include "ash/shell.h"
 #include "ash/style/ash_color_provider.h"
-#include "ash/style/default_color_constants.h"
 #include "ash/system/session/logout_confirmation_controller.h"
 #include "ash/system/status_area_widget.h"
 #include "ash/system/tray/tray_constants.h"
@@ -40,9 +39,9 @@
   auto button = views::MdTextButton::Create(this, base::string16(),
                                             CONTEXT_LAUNCHER_BUTTON);
   button->SetProminent(true);
-  button->SetBgColorOverride(
-      AshColorProvider::Get()->DeprecatedGetBaseLayerColor(
-          AshColorProvider::BaseLayerType::kRed, kLogoutButtonTrayColor));
+  button->SetBgColorOverride(AshColorProvider::Get()->GetBaseLayerColor(
+      AshColorProvider::BaseLayerType::kRed,
+      AshColorProvider::AshColorMode::kDark));
 
   button_ = tray_container()->AddChildView(std::move(button));
 }