Extract colors from wallpaper and dynamically update login screen overlay

chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h

Index: chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h
diff --git a/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h b/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h
index d5256e2e3c8f32c8ddf6e6ae54dc6247abb2e53f..6dad82fa219220c34f11defe41ad0eff0930c821 100644
--- a/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h
+++ b/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h
@@ -30,6 +30,7 @@
 #include "chromeos/network/portal_detector/network_portal_detector.h"
 #include "components/proximity_auth/screenlock_bridge.h"
 #include "components/user_manager/user_manager.h"
+#include "components/wallpaper/wallpaper_color_calculator_observer.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 #include "content/public/browser/web_ui.h"
@@ -239,7 +240,8 @@ class SigninScreenHandler
       public input_method::ImeKeyboard::Observer,
       public ash::mojom::TouchViewObserver,
       public lock_screen_apps::StateObserver,
-      public OobeUI::Observer {
+      public OobeUI::Observer,
+      public wallpaper::WallpaperColorCalculatorObserver {
  public:
   SigninScreenHandler(
       const scoped_refptr<NetworkStateInformer>& network_state_informer,
@@ -277,6 +279,9 @@ class SigninScreenHandler
   void OnCurrentScreenChanged(OobeScreen current_screen,
                               OobeScreen new_screen) override;
 
+  // wallpaper::WallpaperColorCalculatorObserver implementation.
+  void OnColorCalculationComplete() override;
+
   void SetFocusPODCallbackForTesting(base::Closure callback);
 
   // To avoid spurious error messages on flaky networks, the offline message is