When I was investigating flaky 'gclient runhooks' failures for the "Deterministic Linux" bot (bug 727559) I found that some of the failures were due to inability to download from Google storage.

Example: https://build.chromium.org/p/chromium.linux/builders/Deterministic%20Linux/builds/3173

Somehow this bot (only) always downloads everything during 'gclient runhooks', no matter if it was done in the previous build. I know it's a clobber bot that wipes everything in out/Release but the files in question are not located there so I don't know what's going on there.

One of two things must be happening here:
1) The VM is reimaged between each build - seems unlikely but I don't know how to verify that.
2) A completely new checkout is created for each build. I don't know why it would do that? I'm unable to see anything special in the recipe [1] except the clobber steps for out/Release

[1]: https://cs.chromium.org/chromium/build/scripts/slave/recipes/swarming/deterministic_build.py