code: private void updateVoiceButton(boolean empty) {
          int visibility = GONE;
          if (mVoiceButtonEnabled && !isIconified() && empty) {
              visibility = VISIBLE;
              mSubmitButton.setVisibility(GONE);
          }
          mVoiceButton.setVisibility(visibility);
      }
docs: Update the visibility of the voice button.  There are actually two voice search modes,
  either of which will activate the button.
  @param empty whether the search query text field is empty. If it is, then the other
  criteria apply to make the voice button visible.