Do not activate system tray bubble by default

ash/aura/wm_shell_aura.cc

Index: ash/aura/wm_shell_aura.cc
diff --git a/ash/aura/wm_shell_aura.cc b/ash/aura/wm_shell_aura.cc
index 20e706e040b0d8fb4cfc93b72676024611b3f319..9d112c51d3804fe69d0474526f653344a57d4e9b 100644
--- a/ash/aura/wm_shell_aura.cc
+++ b/ash/aura/wm_shell_aura.cc
@@ -6,6 +6,7 @@
 
 #include <utility>
 
+#include "ash/aura/key_event_watcher_aura.h"
 #include "ash/aura/pointer_watcher_adapter.h"
 #include "ash/aura/wm_window_aura.h"
 #include "ash/common/session/session_state_delegate.h"
@@ -229,6 +230,10 @@ WmShellAura::CreateImmersiveFullscreenController() {
   return base::MakeUnique<ImmersiveFullscreenController>();
 }
 
+std::unique_ptr<KeyEventWatcher> WmShellAura::CreateKeyEventWatcher() {
+  return base::MakeUnique<KeyEventWatcherAura>();
+}
+
 void WmShellAura::OnOverviewModeStarting() {
   FOR_EACH_OBSERVER(ShellObserver, *shell_observers(),
                     OnOverviewModeStarting());