Create the ScreensaverImagesPolicyHandler class

This CL introduce the basic implementation for the policy handler
responsible of downloading and caching the images referenced by the
managed screensaver policies.

Bug: b/271093532
Doc: go/gb-screensaver-dd
Test: ./unit_tests --gtest_filter=*ScreensaverImagesPolicyHandlerTest*
Test: ./browser_tests --gtest_filter=*PolicyPrefsTest.PolicyToPrefsMapping*
Test: ./browser_tests --gtest_filter=*SigninPolicyPrefsTest.PolicyToPrefsMapping*
Change-Id: I02cd0c990c6f238dd46d5569ed1a0d7998d64d0d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4341610
Reviewed-by: Xiaohui Chen <[email protected]>
Reviewed-by: Dominic Battré <[email protected]>
Reviewed-by: Mitsuru Oshima <[email protected]>
Reviewed-by: Roman Sorokin <[email protected]>
Commit-Queue: Emmanuel Arias Soto <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1119814}
diff --git a/chrome/browser/prefs/browser_prefs.cc b/chrome/browser/prefs/browser_prefs.cc
index 0230c85..d5c20db 100644
--- a/chrome/browser/prefs/browser_prefs.cc
+++ b/chrome/browser/prefs/browser_prefs.cc
@@ -382,6 +382,7 @@
 #include "chrome/browser/ash/policy/external_data/handlers/device_wallpaper_image_external_data_handler.h"
 #include "chrome/browser/ash/policy/handlers/adb_sideloading_allowance_mode_policy_handler.h"
 #include "chrome/browser/ash/policy/handlers/minimum_version_policy_handler.h"
+#include "chrome/browser/ash/policy/handlers/screensaver_images_policy_handler.h"
 #include "chrome/browser/ash/policy/handlers/tpm_auto_update_mode_policy_handler.h"
 #include "chrome/browser/ash/policy/reporting/app_install_event_log_manager_wrapper.h"
 #include "chrome/browser/ash/policy/reporting/arc_app_install_event_logger.h"
@@ -1466,6 +1467,7 @@
   extensions::ExtensionsUI::RegisterProfilePrefs(registry);
 #if BUILDFLAG(IS_CHROMEOS_ASH)
   extensions::shared_storage::RegisterProfilePrefs(registry);
+  policy::ScreensaverImagesPolicyHandler::RegisterPrefs(registry);
 #endif  // BUILDFLAG(IS_CHROMEOS_ASH)
   extensions::PermissionsManager::RegisterProfilePrefs(registry);
   extensions::RuntimeAPI::RegisterPrefs(registry);