[SessionStorage] Added const to EraseIf

R=pwnall@chromium.org

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

content/renderer/dom_storage/local_storage_cached_areas.cc

@@ -181,7 +181,7 @@ size_t LocalStorageCachedAreas::DOMStorageNamespace::TotalCacheSize() const {
 bool LocalStorageCachedAreas::DOMStorageNamespace::CleanUpUnusedAreas() {
   CheckPrefixes();
   base::EraseIf(cached_areas,
-                [](auto& pair) { return pair.second->HasOneRef(); });
+                [](const auto& pair) { return pair.second->HasOneRef(); });
   return cached_areas.empty();
 }