[SessionStorage] Added const to EraseIf

R=pwnall@chromium.org

Bug: 857464
Change-Id: I14a530854764fb07c875a5b1a19ce35359a662fb
Reviewed-on: https://chromium-review.googlesource.com/1150838
Reviewed-by: Chase Phillips <cmp@chromium.org>
Commit-Queue: Daniel Murphy <dmurph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578174}
1 file changed