enter_chroot: copy application_default_credentials.json to chroot

This is beginning step of http://go/reclient_build_packages_for_chrome

Although we are still discussing where we put reclient, I think we
need to use gcloud auth for reclient as prod auth is not available in
chroot.

ref: http://go/chromium-devs-auth-to-rbe

BUG=b:203606263
TEST=confirms cros_sdk copies the credential file.
Change-Id: I03e1686dc77ff13456ba4ee5ddb9433974ccedf1
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/3774284
Tested-by: Takuto Ikuta <tikuta@chromium.org>
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
diff --git a/sdk_lib/enter_chroot.sh b/sdk_lib/enter_chroot.sh
index ab65ebd..90306e0 100755
--- a/sdk_lib/enter_chroot.sh
+++ b/sdk_lib/enter_chroot.sh
@@ -83,6 +83,10 @@
 FILES_TO_COPY_TO_CHROOT=(
   # Creds used to authenticate with LUCI services.
   .config/chrome_infra/auth/creds.json
+
+  # Creds used to authenticate with GCP services.
+  .config/gcloud/application_default_credentials.json
+
   .gdata_cred.txt             # User/password for Google Docs on chromium.org
   .gdata_token                # Auth token for Google Docs on chromium.org
   .goma_client_oauth2_config  # Auth token for Goma