ios: Extend MetricKit MemoryFootprint FirstUserAction and CrashReport histograms.

Bug: 1235542, 1230704, 1230684, 1228305
Change-Id: I4794798614fd1f7fd63203f7e24c3373afa710de
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3068022


Auto-Submit: Justin Cohen <justincohen@chromium.org>
Commit-Queue: Steven Holte <holte@chromium.org>
Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Cr-Commit-Position: refs/heads/master@{#908687}