Revert of Change how the quota system computes the total poolsize for temporary storage

storage/browser/quota/usage_tracker.cc

Index: storage/browser/quota/usage_tracker.cc
diff --git a/storage/browser/quota/usage_tracker.cc b/storage/browser/quota/usage_tracker.cc
index a29004e06df6e41d97dcaf4fbca491b0b873f10a..041f94067ae40eeeddd88ae620284c190853e298 100644
--- a/storage/browser/quota/usage_tracker.cc
+++ b/storage/browser/quota/usage_tracker.cc
@@ -136,13 +136,6 @@ void UsageTracker::UpdateUsageCache(QuotaClient::ID client_id,
   client_tracker->UpdateUsageCache(origin, delta);
 }
 
-int64_t UsageTracker::GetCachedUsage() const {
-  int64_t usage = 0;
-  for (const auto& client_id_and_tracker : client_tracker_map_)
-    usage += client_id_and_tracker.second->GetCachedUsage();
-  return usage;
-}
-
 void UsageTracker::GetCachedHostsUsage(
     std::map<std::string, int64_t>* host_usage) const {
   DCHECK(host_usage);