Add unit test for memory eviction status

A previous change added logic to record proactive memory evictions
(`TERMINATION_STATUS_EVICTED_FOR_MEMORY`) as renderer crashes for
stability monitoring. However, that change was missing test coverage.

This patch adds a unit test to `StabilityMetricsHelperTest` to verify
this behavior. Additionally, it updates the comment for
`LogRendererCrashImpl` to correctly list
`TERMINATION_STATUS_EVICTED_FOR_MEMORY` as one of the statuses it
handles.

Bug: 394092280

Change-Id: I948204d3268b4fcd2b155b97213d8b9f30b8b4c3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6995421
Reviewed-by: Francois Pierre Doray <fdoray@chromium.org>
Commit-Queue: Alex Attar <aattar@google.com>
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1523221}
NOKEYCHECK=True
GitOrigin-RevId: 9e0797022d206022f96d8d5ba450d8df31fb9b62