[ChromeOS] Add device wallpaper policy handler to ensure the policy display correctly in chrome://p…

chrome/browser/policy/configuration_policy_handler_list_factory.cc

Index: chrome/browser/policy/configuration_policy_handler_list_factory.cc
diff --git a/chrome/browser/policy/configuration_policy_handler_list_factory.cc b/chrome/browser/policy/configuration_policy_handler_list_factory.cc
index d419d89617ab967cc393b067617d191c8a235dd0..0a8a0866b33ef821cfd9d5d060a7872307445dfe 100644
--- a/chrome/browser/policy/configuration_policy_handler_list_factory.cc
+++ b/chrome/browser/policy/configuration_policy_handler_list_factory.cc
@@ -949,6 +949,8 @@ std::unique_ptr<ConfigurationPolicyHandlerList> BuildHandlerList(
   handlers->AddHandler(
       base::MakeUnique<ExternalDataPolicyHandler>(key::kUserAvatarImage));
   handlers->AddHandler(
+      base::MakeUnique<ExternalDataPolicyHandler>(key::kDeviceWallpaperImage));
+  handlers->AddHandler(
       base::MakeUnique<ExternalDataPolicyHandler>(key::kWallpaperImage));
   handlers->AddHandler(base::WrapUnique(new SimpleSchemaValidatingPolicyHandler(
       key::kSessionLocales, NULL, chrome_schema, SCHEMA_STRICT,