Fix stack tool when packed relocations exist and built with GN

BUG=none

Review URL: https://codereview.chromium.org/1828953003

Cr-Original-Commit-Position: refs/heads/master@{#383978}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 28ab0e6e04911af66c935e963a2970ff0f7b45f6