assistant: Hide invisible elements to avoid triggering screenreader

When Views are invisible by opacity 0 but still have visibility true,
screenreader would still be able to read it. We need to explicitly
set their visibility to false.

Bug: b:113731925
Test: locally build and not able to navigate to these elements with
Test: screen reader
Change-Id: Ibb1b111844dbd6021c267ef594777614cf127189
Reviewed-on: https://chromium-review.googlesource.com/1212342Reviewed-by: Muyuan Li <muyuanli@chromium.org>
Commit-Queue: Xiaohui Chen <xiaohuic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590085}

ash/assistant/ui/dialog_plate/dialog_plate.cc

@@ -146,6 +146,9 @@ void DialogPlate::OnInputModalityChanged(InputModality input_modality) {
   using assistant::util::CreateTransformElement;
   using assistant::util::StartLayerAnimationSequencesTogether;
 
+  keyboard_layout_container_->SetVisible(true);
+  voice_layout_container_->SetVisible(true);
+
   switch (input_modality) {
     case InputModality::kKeyboard: {
       // Animate voice layout container opacity to 0%.
@@ -387,15 +390,16 @@ bool DialogPlate::OnAnimationEnded(
   InputModality input_modality = assistant_controller_->interaction_controller()
                                      ->model()
                                      ->input_modality();
-  SetFocusMode(input_modality);
   SetFocus(input_modality);
 
   switch (input_modality) {
     case InputModality::kKeyboard:
       keyboard_layout_container_->set_can_process_events_within_subtree(true);
+      voice_layout_container_->SetVisible(false);
       break;
     case InputModality::kVoice:
       voice_layout_container_->set_can_process_events_within_subtree(true);
+      keyboard_layout_container_->SetVisible(false);
       break;
     case InputModality::kStylus:
       // No action necessary.
@@ -420,24 +424,4 @@ void DialogPlate::SetFocus(InputModality input_modality) {
   }
 }
 
-void DialogPlate::SetFocusMode(InputModality input_modality) {
-  switch (input_modality) {
-    case InputModality::kKeyboard:
-      textfield_->SetFocusBehavior(FocusBehavior::ALWAYS);
-      voice_input_toggle_->SetFocusBehavior(FocusBehavior::ALWAYS);
-      keyboard_input_toggle_->SetFocusBehavior(FocusBehavior::NEVER);
-      animated_voice_input_toggle_->SetFocusBehavior(FocusBehavior::NEVER);
-      break;
-    case InputModality::kVoice:
-      textfield_->SetFocusBehavior(FocusBehavior::NEVER);
-      voice_input_toggle_->SetFocusBehavior(FocusBehavior::NEVER);
-      keyboard_input_toggle_->SetFocusBehavior(FocusBehavior::ALWAYS);
-      animated_voice_input_toggle_->SetFocusBehavior(FocusBehavior::ALWAYS);
-      break;
-    case InputModality::kStylus:
-      // No action necessary.
-      break;
-  }
-}
-
 }  // namespace ash

ash/assistant/ui/dialog_plate/dialog_plate.h

@@ -105,7 +105,6 @@ class DialogPlate : public views::View,
   bool OnAnimationEnded(const ui::CallbackLayerAnimationObserver& observer);
 
   void SetFocus(InputModality modality);
-  void SetFocusMode(InputModality modality);
 
   AssistantController* const assistant_controller_;  // Owned by Shell.