Enable "Let me choose what to sync" checkbox in gaia sign in page.

chrome/browser/ui/webui/sync_setup_handler.cc

Index: chrome/browser/ui/webui/sync_setup_handler.cc
diff --git a/chrome/browser/ui/webui/sync_setup_handler.cc b/chrome/browser/ui/webui/sync_setup_handler.cc
index 004516295b4a739045955b10b6334aebe77e137a..fe275f9895d07f0a983a12b7936bef60ebf59660 100644
--- a/chrome/browser/ui/webui/sync_setup_handler.cc
+++ b/chrome/browser/ui/webui/sync_setup_handler.cc
@@ -1051,6 +1051,9 @@ void SyncSetupHandler::CloseSyncSetup() {
     }
 
     // Let the various services know that we're no longer active.
+    if (SyncPromoUI::UseWebBasedSigninFlow())
+      CloseGaiaSigninPage();
+
     GetLoginUIService()->LoginUIClosed(this);
   }