Display the InstructionSequence before and after register allocation.

Change-Id: If5169ae1af4f1fda95b3d150f9318ad11679caee
Reviewed-on: https://chromium-review.googlesource.com/c/1258005
Commit-Queue: Martyn Capewell <martyn.capewell@arm.com>
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56451}