Also includes some tracking of if a cache hit comes from a binary
inserted after a Link call, or sourced from the external disk cache.

Chromium-side CL: https://chromium-review.googlesource.com/c/592151/

BUG=angleproject:2118

Change-Id: I80eefd203d8ce31d1ac03dd1a36459d3581128f5
Reviewed-on: https://chromium-review.googlesource.com/590689
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>