Bump timeout of telemetry_perf_unittests shards on android-marshmallow-arm64-rel.

From 16min to 30min.

The suite has some very uneven sharding. Some shard finish in 300s, some
in 900s:
https://ci.chromium.org/p/chromium/builders/luci.chromium.try/android-marshmallow-arm64-rel/169047

No try to alleviate the CQ bot.
NOTRY=true

Bug: 921662
Change-Id: Id44f10013604aab164164ff55a154d5dd54be058
Reviewed-on: https://chromium-review.googlesource.com/c/1415436
Reviewed-by: Caleb Rouleau <crouleau@chromium.org>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#623363}
2 files changed