Add layers to proto by traversing children

There are currently some layers that end up missing from the proto dumps
since their relativeOf layer has been deleted. That means the layers are
still in memory, but not traversable since we skip layers that have a
relativeOf when traversing. Instead, we can traverse the children
directly.

Test: Layers will missing relativeOf are adding to proto
Change-Id: I571ef677de0544dfe7459080cf97ff193e8666e6