When printing the number and size of the instance types in each
snapshot, break out each line into the number for each AllocationSpace.

(This removes the specific RO_SPACE path that just broke out its stats).

Change-Id: I9d5bcecc4f0e8e1ec5c83409f54164f9bf83c5be
Reviewed-on: https://chromium-review.googlesource.com/1175826Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55184}