assistant: Add stop button to timer notification

This cl add a STOP button to timer notification.

Bug: b/118655426
Test: manual
Change-Id: I88752010e4b0c5be54debddb8394827a798d65fe
Reviewed-on: https://chromium-review.googlesource.com/c/1330296Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Tao Wu <wutao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607007}

chromeos/chromeos_strings.grd

@@ -136,6 +136,9 @@ Try tapping the mic to ask me anything.
       <message name="IDS_ASSISTANT_STOP_TIMER_QUERY" desc="Query for stopping assistant timer.">
         Stop timer
       </message>
+      <message name="IDS_ASSISTANT_STOP_BUTTON_TEXT" desc="Text shown on stop button in Assistant timer notification.">
+        STOP
+      </message>
 
       <!-- The following strings are located here for accessibility from both //ash and //chrome -->
       <message name="IDS_ENABLE_BLUETOOTH" desc="The message to display in the network list when Tether is enabled but Bluetooth is disabled.">

chromeos/services/assistant/assistant_manager_service_impl.cc

@@ -914,15 +914,18 @@ void AssistantManagerServiceImpl::OnTimerSoundingStarted() {
   const std::string stop_timer_query =
       l10n_util::GetStringUTF8(IDS_ASSISTANT_STOP_TIMER_QUERY);
 
+  const std::string action_url = kQueryDeeplinkPrefix + stop_timer_query;
   action::Notification notification(
       /*title=*/notification_title,
       /*text=*/notification_content,
-      /*action_url=*/kQueryDeeplinkPrefix + stop_timer_query,
+      /*action_url=*/action_url,
       /*notification_id=*/{},
       /*consistency_token=*/{},
       /*opaque_token=*/{},
       /*grouping_key=*/kTimerFireNotificationGroupId,
-      /*obfuscated_gaia_id=*/{});
+      /*obfuscated_gaia_id=*/{},
+      /*buttons=*/
+      {{l10n_util::GetStringUTF8(IDS_ASSISTANT_STOP_BUTTON_TEXT), action_url}});
   OnShowNotification(notification);
 }