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Adds --pregenerated-profiles and --profile-save-dir to
orderfile_generator_backend.py. These allow for precise comparisons
between different versions of profile processing, that are not affected
by variations in the symbols seen during device profiling.

Bug: 869997
Change-Id: I9dd734a77ea4a738e22f20f095e76879e71f3c0c
Reviewed-on: https://chromium-review.googlesource.com/1162179
Commit-Queue: Matthew Cary <mattcary@chromium.org>
Reviewed-by: Egor Pasko <pasko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#582258}