Add field trial param to suppress disallowed subresource notifications.

components/subresource_filter/content/browser/content_subresource_filter_driver_factory.cc

Index: components/subresource_filter/content/browser/content_subresource_filter_driver_factory.cc
diff --git a/components/subresource_filter/content/browser/content_subresource_filter_driver_factory.cc b/components/subresource_filter/content/browser/content_subresource_filter_driver_factory.cc
index 78935d5a6ea572bf667270628a669398085b95d7..63942318cad19a17b64dea4d4347e6738d5d50c9 100644
--- a/components/subresource_filter/content/browser/content_subresource_filter_driver_factory.cc
+++ b/components/subresource_filter/content/browser/content_subresource_filter_driver_factory.cc
@@ -88,6 +88,9 @@ void ContentSubresourceFilterDriverFactory::CreateDriverForFrameHostIfNeeded(
 }
 
 void ContentSubresourceFilterDriverFactory::OnFirstSubresourceLoadDisallowed() {
+  if (ShouldSuppressNotifications())
+    return;
+
   client_->ToggleNotificationVisibility(activation_level_ ==
                                         ActivationLevel::ENABLED);
 }