[CSC] Implement promo handler for MSBB

This CL:
- Adds promo handler implementation.
- Introduces prefs to persist user actions on the promo.
- Turns on MSBB for the MSBB promo.

Bug: b:273969630
Change-Id: Id3159d8e234cfb60fac5abecd670ee32a5c4242d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4356554
Reviewed-by: Michael Crouse <[email protected]>
Commit-Queue: Shakti Sahu <[email protected]>
Reviewed-by: Ali Stanfield <[email protected]>
Reviewed-by: Dominic Battré <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1122876}
diff --git a/chrome/browser/prefs/browser_prefs.cc b/chrome/browser/prefs/browser_prefs.cc
index bc34265..661e7625 100644
--- a/chrome/browser/prefs/browser_prefs.cc
+++ b/chrome/browser/prefs/browser_prefs.cc
@@ -278,6 +278,7 @@
 #include "chrome/browser/ui/webui/new_tab_page/new_tab_page_handler.h"
 #include "chrome/browser/ui/webui/new_tab_page/new_tab_page_ui.h"
 #include "chrome/browser/ui/webui/settings/settings_ui.h"
+#include "chrome/browser/ui/webui/side_panel/companion/promo_handler.h"
 #include "chrome/browser/ui/webui/side_panel/read_anything/read_anything_prefs.h"
 #include "chrome/browser/ui/webui/tab_search/tab_search_prefs.h"
 #include "chrome/browser/ui/webui/whats_new/whats_new_ui.h"
@@ -1531,6 +1532,7 @@
   BrowserFeaturePromoSnoozeService::RegisterProfilePrefs(registry);
   captions::LiveTranslateController::RegisterProfilePrefs(registry);
   ChromeAuthenticatorRequestDelegate::RegisterProfilePrefs(registry);
+  companion::PromoHandler::RegisterProfilePrefs(registry);
   DeviceServiceImpl::RegisterProfilePrefs(registry);
   DevToolsWindow::RegisterProfilePrefs(registry);
   DriveService::RegisterProfilePrefs(registry);