Add DCHECK to address a comment in CL:1548974

BUG=921357
TEST=try

Change-Id: I05b426832e5de4d1a2d5d340b408fdc06e9b97ab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1579560
Commit-Queue: Fran├žois Doray <fdoray@chromium.org>
Reviewed-by: Fran├žois Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653377}
1 file changed