Remove ArcImeService from window observers on shutdown

components/arc/ime/arc_ime_service.cc

Index: components/arc/ime/arc_ime_service.cc
diff --git a/components/arc/ime/arc_ime_service.cc b/components/arc/ime/arc_ime_service.cc
index c658587d27aaaf71920bbe071e8ba94a2e379892..9259f31aad29e083415249ddb1dc897270a5f615 100644
--- a/components/arc/ime/arc_ime_service.cc
+++ b/components/arc/ime/arc_ime_service.cc
@@ -74,6 +74,8 @@ ArcImeService::~ArcImeService() {
   if (input_method)
     input_method->DetachTextInputClient(this);
 
+  if (focused_arc_window_)
+    focused_arc_window_->RemoveObserver(this);
   if (is_focus_observer_installed_)
     arc_window_delegate_->UnregisterFocusObserver();
   aura::Env* env = aura::Env::GetInstanceDontCreate();