Add histograms for the program cache. 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>