Commit c86f1897 corrected the way context from which a specific error is
thrown, but the in-line comment was not updated to reflect this.

Update the comment to accurately describe the intended behavior.

LOG=N
R=littledan@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/1999483002
Cr-Commit-Position: refs/heads/master@{#36541}