events: adds base::debug::Alias to see event type in crashes

I'm hoping knowing the event type will at least help identify
what might be going wrong in some way.

BUG=867035
TEST=none

Change-Id: I78109f72b27d932e1754a24fd0f8af5d81b86b0f
Reviewed-on: https://chromium-review.googlesource.com/1161165Reviewed-by: James Cook <jamescook@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#580352}

ui/events/event_handler.cc

@@ -4,6 +4,7 @@
 
 #include "ui/events/event_handler.h"
 
+#include "base/debug/alias.h"
 #include "ui/events/event.h"
 #include "ui/events/event_dispatcher.h"
 
@@ -21,6 +22,10 @@ EventHandler::~EventHandler() {
 }
 
 void EventHandler::OnEvent(Event* event) {
+  // TODO(sky): remove |event_type|. Temporary while tracking down crash.
+  // https://crbug.com/867035
+  const EventType event_type = event->type();
+  base::debug::Alias(&event_type);
   if (event->IsKeyEvent())
     OnKeyEvent(event->AsKeyEvent());
   else if (event->IsMouseEvent())