android: Add reverse rank uma

Record the reverse rank of android killed child processes.

Bug: 946216
Change-Id: I844bed1b8219b711a301952a808160f61ffab1ca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1603056
Commit-Queue: Bo <boliu@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Reviewed-by: ssid <ssid@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659781}
13 files changed