Add ability for Widgets to override the DefaultThemeProvider

chrome/browser/chromeos/login/ui/login_display_host_impl.cc

Index: chrome/browser/chromeos/login/ui/login_display_host_impl.cc
diff --git a/chrome/browser/chromeos/login/ui/login_display_host_impl.cc b/chrome/browser/chromeos/login/ui/login_display_host_impl.cc
index ae9d5658b54785dccebd2a9b6c24d4c10a5518a3..5c4fce3c83d250d63225ef92f8d70d6efc836a47 100644
--- a/chrome/browser/chromeos/login/ui/login_display_host_impl.cc
+++ b/chrome/browser/chromeos/login/ui/login_display_host_impl.cc
@@ -56,6 +56,9 @@
 #include "chrome/browser/chromeos/ui/focus_ring_controller.h"
 #include "chrome/browser/lifetime/application_lifetime.h"
 #include "chrome/browser/profiles/profile_manager.h"
+#include "chrome/browser/themes/theme_service.h"
+#include "chrome/browser/themes/theme_service_factory.h"
+#include "chrome/browser/ui/ash/multi_user/multi_user_util.h"
 #include "chrome/browser/ui/webui/chromeos/login/oobe_ui.h"
 #include "chrome/common/chrome_constants.h"
 #include "chrome/common/chrome_switches.h"
@@ -1018,6 +1021,13 @@ void LoginDisplayHostImpl::InitLoginWindowAndView() {
   params.parent =
       ash::Shell::GetContainer(ash::Shell::GetPrimaryRootWindow(),
                                ash::kShellWindowId_LockScreenContainer);

[oshima, 2015/09/10 00:20:38]

this parent will never have associated profile. The screen is always locked by
the 1st user, so i guess you have to use that?

+  // On login screen and logged in as an anonymous user you might not get a
+  // profile. Which indicates that multi-user is not active and an anonymous
+  // profile is in use. Take the active profile to find the theme.
+  Profile* profile = multi_user_util::GetProfileFromWindow(params.parent);
+  if (!profile)
+    profile = ProfileManager::GetActiveUserProfile();
+  params.theme_provider = ThemeServiceFactory::GetForProfile(profile);
   login_window_ = new views::Widget;
   params.delegate = new LoginWidgetDelegate(login_window_);
   login_window_->Init(params);