Remove unused/unnecessary code from the external protocol dialog for ARC

chrome/browser/chromeos/arc/arc_external_protocol_dialog.cc

Index: chrome/browser/chromeos/arc/arc_external_protocol_dialog.cc
diff --git a/chrome/browser/chromeos/arc/arc_external_protocol_dialog.cc b/chrome/browser/chromeos/arc/arc_external_protocol_dialog.cc
index a7a8f55eeb39ddc96b9a4486317944d51b6380d5..883cf4a41a4537ebe9428f197543c8881a962153 100644
--- a/chrome/browser/chromeos/arc/arc_external_protocol_dialog.cc
+++ b/chrome/browser/chromeos/arc/arc_external_protocol_dialog.cc
@@ -75,18 +75,21 @@ void OnIntentPickerClosed(int render_process_host_id,
 
   switch (close_reason) {
     case ArcNavigationThrottle::CloseReason::ALWAYS_PRESSED: {
-      intent_helper->AddPreferredPackage(
-          handlers[selected_app_index]->package_name);
-      // fall through.
+      // TODO(yusukes): Add NOTREACHED(); break; here once b/31665510 is fixed.
+      // fall through, for now.
     }
-    case ArcNavigationThrottle::CloseReason::JUST_ONCE_PRESSED:
-    case ArcNavigationThrottle::CloseReason::PREFERRED_ACTIVITY_FOUND: {
+    case ArcNavigationThrottle::CloseReason::JUST_ONCE_PRESSED: {
       // Launch the selected app.
       intent_helper->HandleUrl(url.spec(),
                                handlers[selected_app_index]->package_name);
       CloseTabIfNeeded(render_process_host_id, routing_id);
       break;
     }
+    case ArcNavigationThrottle::CloseReason::PREFERRED_ACTIVITY_FOUND: {
+      // Our OnUrlHandlerList callback does not search for a preferred activity.
+      NOTREACHED();
+      break;
+    }
     case ArcNavigationThrottle::CloseReason::ERROR:
     case ArcNavigationThrottle::CloseReason::INVALID: {
       LOG(ERROR) << "IntentPickerBubbleView returned unexpected close_reason: "