Turns out gclient calls download_from_google_storage, which needs to be
included in PATH.

TBR=machenbach@chromium.org

Bug: v8:6105
Change-Id: I15d44d67152f6fa0d20ae7bc7e44bc5e0393b519
Reviewed-on: https://chromium-review.googlesource.com/852616Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50389}