SyncFrame: Adapt sync_time_ to avoid TF extrapolation
SyncFrame: Adapt sync_time_ to avoid TF extrapolation

In SyncFrame mode, we use ros::Time::now() for syncing, which is typically
more recent than any TF stamp available, causing extrapolationn exceptions.
To avoid that, we date back sync_time_ by a small amount sync_delta_, that
is determined from observed lookup time differences.

ros-visualization/rviz,ros-visualization/rviz,ros-visualization/rviz,ros-visualization/rviz,ros-visualization/rviz