base: Add status for proactive memory-saving terminations

It is necessary to distinguish between a process that crashed due to
memory issues and one that was proactively terminated by the browser to
prevent a future out-of-memory (OOM) situation. The existing statuses
did not capture this distinction.

This change introduces `TERMINATION_STATUS_EVICTED_FOR_MEMORY` to
identify these proactive, memory-saving terminations.

Functionally, this change is a no-op. The new status is handled
identically to `TERMINATION_STATUS_OOM`, causing a "sad tab" to be
displayed. This lays the groundwork for future work to handle these
evictions with a different user experience, such as treating them as tab
discards.

Bug: 394092280

Change-Id: I3bce03bc1e5017eecf3fa8710d459771c6c950f6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6991933
Commit-Queue: Francois Pierre Doray <fdoray@chromium.org>
Owners-Override: Francois Pierre Doray <fdoray@chromium.org>
Reviewed-by: Francois Pierre Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1522312}
NOKEYCHECK=True
GitOrigin-RevId: a2100e2ad5a1d3fd45c71b060f4889f9d95c6d8e