Use total charge in MaintainPoolSize (#5813)

Summary:
https://github.com/facebook/rocksdb/issues/5797 charges the block cache with the total of user-provided charge plus the metadata charge. It had a bug where in MaintainPoolSize the user-provided charge was used instead of the total charge. The patch fixes that.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5813

Differential Revision: D17412783

Pulled By: maysamyabandeh

fbshipit-source-id: 45c0ac9f1e2233760db5ccd61399605cd74edc87

cache/lru_cache.cc

@@ -225,8 +225,10 @@ void LRUCacheShard::MaintainPoolSize() {
     lru_low_pri_ = lru_low_pri_->next;
     assert(lru_low_pri_ != &lru_);
     lru_low_pri_->SetInHighPriPool(false);
-    assert(high_pri_pool_usage_ >= lru_low_pri_->charge);
+    size_t total_charge =
-    high_pri_pool_usage_ -= lru_low_pri_->charge;
+        lru_low_pri_->CalcTotalCharge(metadata_charge_policy_);
+    assert(high_pri_pool_usage_ >= total_charge);
+    high_pri_pool_usage_ -= total_charge;
   }
 }