diagnostics: Disable run CPU tests button when available memory < 625 MB

Screenshot: https://screenshot.googleplex.com/5Ss2NtJxyy7bCf5

Bug: b/271061014
Change-Id: I20a2d850bbf8aec3ee028e7597cdf29ad6a1e72f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4563357


Commit-Queue: Camden Bickel <cambickel@google.com>
Reviewed-by: Michael Checo <michaelcheco@google.com>
Cr-Commit-Position: refs/heads/main@{#1149428}