Set a continuous reporting spec for MetricsReporterTest#SampleRate* tests am: 9b79e11288 am: ff0ae2db9c am: 3f9f0427e8 am: 59f0f17486

Original change: https://android-review.googlesource.com/c/platform/art/+/2200424

Change-Id: I063512629f123547719da0596fcfa32ee2936512
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>