Purge new localstorage memory cache when under memory pressure.

content/browser/leveldb_wrapper_impl.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/leveldb_wrapper_impl.h"
 
 #include "base/bind.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "components/leveldb/public/cpp/util.h"
@@ skipping 71 matching lines @@
     LoadMap(base::Bind(&LevelDBWrapperImpl::ScheduleImmediateCommit,
                        base::Unretained(this)));
     return;
   }
 
   if (!database_ || !commit_batch_)
     return;
   CommitChanges();
 }
 
+void LevelDBWrapperImpl::PurgeMemory() {
+  if (!map_ ||          // We're not using any memory.
+      commit_batch_ ||  // We leave things alone with changes pending.
+      !database_) {  // Don't purge anything if we're not backed by a database.
+    return;
+  }
+
+  map_.reset();
+}
+
 void LevelDBWrapperImpl::AddObserver(
     mojom::LevelDBObserverAssociatedPtrInfo observer) {
   mojom::LevelDBObserverAssociatedPtr observer_ptr;
   observer_ptr.Bind(std::move(observer));
   observers_.AddPtr(std::move(observer_ptr));
 }
 
 void LevelDBWrapperImpl::Put(const std::vector<uint8_t>& key,
                              const std::vector<uint8_t>& value,
                              const std::string& source,
@@ skipping 324 matching lines @@
                               weak_ptr_factory_.GetWeakPtr()));
 }
 
 void LevelDBWrapperImpl::OnCommitComplete(leveldb::mojom::DatabaseError error) {
   --commit_batches_in_flight_;
   StartCommitTimer();
   delegate_->DidCommit(error);
 }
 
 }  // namespace content