Dismiss the opt-in dialog if the Assistant is disabled

If the user disable the Assistant when the opt-in dialog is showing up,
the dialog should be dismissed.

Bug: b/152283171
Test: Manual Test
Change-Id: Iecb9a309f839fd6dbbcb80e82597376658a2ce3f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2121036Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Yue Li <updowndota@chromium.org>
Cr-Commit-Position: refs/heads/master@{#753829}

chrome/browser/ui/webui/chromeos/login/assistant_optin_flow_screen_handler.cc

@@ -275,6 +275,12 @@ void AssistantOptInFlowScreenHandler::OnDialogClosed() {
   }
 }
 
+void AssistantOptInFlowScreenHandler::OnAssistantSettingsEnabled(bool enabled) {
+  // Close the opt-in screen is the Assistant is disabled.
+  if (!enabled)
+    HandleFlowFinished();
+}
+
 void AssistantOptInFlowScreenHandler::OnAssistantStatusChanged(
     ash::mojom::AssistantState state) {
   if (state != ash::mojom::AssistantState::NOT_READY) {

chrome/browser/ui/webui/chromeos/login/assistant_optin_flow_screen_handler.h

@@ -96,6 +96,7 @@ class AssistantOptInFlowScreenHandler
   void Initialize() override;
 
   // ash::AssistantStateObserver:
+  void OnAssistantSettingsEnabled(bool enabled) override;
   void OnAssistantStatusChanged(ash::mojom::AssistantState state) override;
 
   // Connect to assistant settings manager.