Allow the cast tray to function as expected when the installed extension is missing API methods.

BUG=489445

Review URL: https://codereview.chromium.org/1145833003

Cr-Commit-Position: refs/heads/master@{#330663}
void CastCastView::UpdateLabel() {
  if (cast_config_delegate_ == nullptr ||
      cast_config_delegate_->HasCastExtension() == false)
    return;

  cast_config_delegate_->GetReceiversAndActivities(
      base::Bind(&CastCastView::UpdateLabelCallback, base::Unretained(this)));
}

void CastCastView::UpdateLabel() {
  if (cast_config_delegate_ == nullptr ||
      cast_config_delegate_->HasCastExtension() == false)
    return;

  cast_config_delegate_->GetReceiversAndActivities(
      base::Bind(&CastCastView::UpdateLabelCallback, base::Unretained(this)));
}
