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}
bool CastConfigDelegateChromeos::HasCastExtension() const {
  return FindCastExtension() != nullptr;
}

bool CastConfigDelegateChromeos::HasCastExtension() const {
  return FindCastExtension() != nullptr;
}
