Reland "[dPWA] Updating linux os integration override to use base::Environment"

This is a reland of commit bda3f49aec7907d00b96e7d6afd159d8c0c39d75

Revert was created by mistake.

Bug: 333387135

Original change's description:
> [dPWA] Updating linux os integration override to use base::Environment
>
> This change migrates the linux os integration unit tests to use the
> override functionality, and upgrades that functionality to integrate
> more deeply with base::Environement, allowing less test-specific code
> in production
>
> Bug: 328437955,b/328524602,b/331633476
> Change-Id: I899d50fef9f9b9758fd794321c2ad8662a81f126
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5425767
> Reviewed-by: Dibyajyoti Pal <dibyapal@chromium.org>
> Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
> Commit-Queue: Daniel Murphy <dmurph@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1283325}

Bug: 328437955,b/328524602,b/331633476
Change-Id: I70ccffcbff0b47f43180e5b2a63435449f8fae22
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5435897
Reviewed-by: Dibyajyoti Pal <dibyapal@chromium.org>
Commit-Queue: Daniel Murphy <dmurph@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1283945}