This helps clarify that the cache is able to take snapshots of its
contents, and this snapshot can be queried without the overhead of
acquiring a mutex.

Bug: b/131246679
Change-Id: I4317628a22f70d37309908b24df62dc5ec5a946c
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/42568
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>