https://build.chromium.org/p/tryserver.chromium.win/builders/win10_chromium_x64_rel_ng_exp has been failing with exception 'ensure_goma.ensure_installed' for almost all of the last 200 builds (some have patch failures).

From the ensure_goma step log: 

[P3128 01:40:04.906 service.go:62 E] Failed to load private key JSON - open C:\creds\service_accounts\service-account-goma-client.json: The system cannot find the file specified.
[P3128 01:40:04.906 remote.go:95 W] cipd: connectivity error (Get https://chrome-infra-packages.appspot.com/_ah/api/repo/v1/instance/resolve?package_name=infra%2Ftools%2Fcloudtail%2Fwindows-amd64&version=goma_recipe_module: open C:\creds\service_accounts\service-account-goma-client.json: The system cannot find the file specified.)
Error: resolving package: failed to resolve package version (line 1): request to the backend failed after multiple attempts.

Example: https://luci-logdog.appspot.com/v/?s=chromium%2Fbb%2Ftryserver.chromium.win%2Fwin10_chromium_x64_rel_ng_exp%2F7166%2F%2B%2Frecipes%2Fsteps%2Fensure_goma%2F0%2Fsteps%2Fensure_installed%2F0%2Fstdout