arc: ime: Fix RequestHideIme condition check.

The condition in ArcImeService::RequestHideIme() didn't properly
recognize if ARC++ window is focused.

TEST=manual
BUG=b/65635084

Change-Id: Ia8edb44af403e2ddafad17fbae90704919ffb21c
Reviewed-on: https://chromium-review.googlesource.com/c/1343470Reviewed-by: Yuichiro Hanada <yhanada@chromium.org>
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609615}

components/arc/ime/arc_ime_service.cc

@@ -323,8 +323,7 @@ void ArcImeService::OnCursorRectChangedWithSurroundingText(
 
 void ArcImeService::RequestHideIme() {
   // Ignore the request when the ARC app is not focused.
-  ui::InputMethod* const input_method = GetInputMethod();
-  if (!input_method || input_method->GetTextInputClient() != nullptr)
+  if (!focused_arc_window_)
     return;
 
   // TODO(mash): Support virtual keyboard under MASH. There is no