message: only implement flushAndWait() debugging on android
  it's causing some unrelated problem on the iOS simulator, and we're
  looking for an Android bug anyways.
diff: @@ -348,13 +348,19 @@ void FEngine::flush() {
  void FEngine::flushAndWait() {
  +#if defined(ANDROID)
  +
  // first make sure we've not terminated filament
  ASSERT_PRECONDITION(!mCommandBufferQueue.isExitRequested(),
  "calling Engine::flushAndWait() after Engine::shutdown()!");
  +#endif
  +
  // enqueue finish command -- this will stall in the driver until the GPU is done
  getDriverApi().finish();
  +#if defined(ANDROID)
  +
  // then create a fence that will trigger when we're past the finish() above
  size_t tryCount = 8;
  FFence* fence = FEngine::createFence(FFence::Type::SOFT);
  @@ -374,6 +380,13 @@ void FEngine::flushAndWait() {
  } while (true);
  destroy(fence);
  +#else
  +
  + FFence::waitAndDestroy(
  + FEngine::createFence(FFence::Type::SOFT), FFence::Mode::FLUSH);
  +
  +#endif
  +
  // finally, execute callbacks that might have been scheduled
  getDriver().purge();
  }
  