Fix regression: empty tooltip appears in Linux and Chrome OS

ui/views/corewm/tooltip_controller.cc

Index: ui/views/corewm/tooltip_controller.cc
diff --git a/ui/views/corewm/tooltip_controller.cc b/ui/views/corewm/tooltip_controller.cc
index a52c806a9928e56dd9a4f212c9535e1e456da06d..bd400e9c30e4c31730872009c9b795c12dbd7331 100644
--- a/ui/views/corewm/tooltip_controller.cc
+++ b/ui/views/corewm/tooltip_controller.cc
@@ -308,6 +308,7 @@ void TooltipController::UpdateIfRequired() {
                          &tooltip_text_whitespace_trimmed_);
     if (tooltip_text_whitespace_trimmed_.empty()) {
       tooltip_->Hide();
+      tooltip_defer_timer_.Stop();
     } else if (tooltip_show_delayed_) {
       // Initialize the one-shot timer to show the tooltip in a while.
       // If there is already a request queued then cancel it and post the new