Do not activate system tray bubble by default

ash/common/wm_shell.h

Index: ash/common/wm_shell.h
diff --git a/ash/common/wm_shell.h b/ash/common/wm_shell.h
index 08c83d483dc145c5a5a469ce1ac8127eaa891767..0a09d084b1a5a2e6a8ebff1d85b1b30003dbf6cc 100644
--- a/ash/common/wm_shell.h
+++ b/ash/common/wm_shell.h
@@ -47,6 +47,7 @@ class BrightnessControlDelegate;
 class FocusCycler;
 class ImmersiveContextAsh;
 class ImmersiveFullscreenController;
+class KeyEventWatcher;
 class KeyboardBrightnessControlDelegate;
 class KeyboardUI;
 class MaximizeModeController;
@@ -308,6 +309,8 @@ class ASH_EXPORT WmShell {
   virtual std::unique_ptr<ImmersiveFullscreenController>
   CreateImmersiveFullscreenController() = 0;
 
+  virtual std::unique_ptr<KeyEventWatcher> CreateKeyEventWatcher() = 0;
+
   void CreateShelfDelegate();
 
   // Called after maximize mode has started, windows might still animate though.