Adds tools/memory to standalone DEPS.

Bug: angleproject:3897
Change-Id: I744e5816156e6e1df78033201eb7fd56083c1bc6
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1787997Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>