fix race condition that can cause a use after free

    // Call back without the main BufferQueue lock held, but with the callback

    // lock held so we can ensure that callbacks occur in order

    {

    int connectedApi;

    sp<Fence> lastQueuedFence;

    { // scope for the lock

        Mutex::Autolock lock(mCallbackMutex);

        while (callbackTicket != mCurrentCallbackTicket) {

            mCallbackCondition.wait(mCallbackMutex);

            frameReplacedListener->onFrameReplaced(item);

        }

        connectedApi = mCore->mConnectedApi;

        lastQueuedFence = std::move(mLastQueueBufferFence);

        mLastQueueBufferFence = std::move(fence);

        mLastQueuedCrop = item.mCrop;

        mLastQueuedTransform = item.mTransform;

        ++mCurrentCallbackTicket;

        mCallbackCondition.broadcast();

    }

    // Wait without lock held

    if (mCore->mConnectedApi == NATIVE_WINDOW_API_EGL) {

    if (connectedApi == NATIVE_WINDOW_API_EGL) {

        // Waiting here allows for two full buffers to be queued but not a

        // third. In the event that frames take varying time, this makes a

        // small trade-off in favor of latency rather than throughput.

        mLastQueueBufferFence->waitForever("Throttling EGL Production");

        lastQueuedFence->waitForever("Throttling EGL Production");

    }

    mLastQueueBufferFence = fence;

    mLastQueuedCrop = item.mCrop;

    mLastQueuedTransform = item.mTransform;

    return NO_ERROR;

}