Add callback to LevelDBWrapperImpl to allow extra operations on commit.

content/browser/leveldb_wrapper_impl.h

 // 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.
 
 #ifndef CONTENT_BROWSER_LEVELDB_WRAPPER_IMPL_H_
 #define CONTENT_BROWSER_LEVELDB_WRAPPER_IMPL_H_
 
 #include <map>
 #include <memory>
 #include <string>
@@ skipping 14 matching lines @@
 // pointers can be bound to the same object. The wrapper adds a couple of
 // features not found directly in leveldb.
 // 1) Adds the given prefix, if any, to all keys. This allows the sharing of one
 //    database across many, possibly untrusted, consumers and ensuring that they
 //    can't access each other's values.
 // 2) Enforces a max_size constraint.
 // 3) Informs observers when values scoped by prefix are modified.
 // 4) Throttles requests to avoid overwhelming the disk.
 class CONTENT_EXPORT LevelDBWrapperImpl : public mojom::LevelDBWrapper {
  public:
+  using PrepareToCommitCallback =
+      base::Callback<std::vector<leveldb::mojom::BatchedOperationPtr>()>;
+
   // |no_bindings_callback| will be called when this object has no more
   // bindings and all pending modifications have been processed.
   LevelDBWrapperImpl(leveldb::mojom::LevelDBDatabase* database,
                      const std::string& prefix,
                      size_t max_size,
                      base::TimeDelta default_commit_delay,
                      int max_bytes_per_hour,
                      int max_commits_per_hour,
-                     const base::Closure& no_bindings_callback);
+                     const base::Closure& no_bindings_callback,
+                     const PrepareToCommitCallback& prepare_to_commit_callback);
   ~LevelDBWrapperImpl() override;
 
   void Bind(mojom::LevelDBWrapperRequest request);
 
   // Commence aggressive flushing. This should be called early during startup,
   // before any localStorage writing. Currently scheduled writes will not be
   // rescheduled and will be flushed at the scheduled time after which
   // aggressive flushing will commence.
   static void EnableAggressiveCommitDelay();
 
@@ skipping 57 matching lines @@
   void CreateCommitBatchIfNeeded();
   void StartCommitTimer();
   base::TimeDelta ComputeCommitDelay() const;
   void CommitChanges();
   void OnCommitComplete(leveldb::mojom::DatabaseError error);
 
   std::vector<uint8_t> prefix_;
   mojo::BindingSet<mojom::LevelDBWrapper> bindings_;
   mojo::AssociatedInterfacePtrSet<mojom::LevelDBObserver> observers_;
   base::Closure no_bindings_callback_;
+  PrepareToCommitCallback prepare_to_commit_callback_;
   leveldb::mojom::LevelDBDatabase* database_;
   std::unique_ptr<ValueMap> map_;
   std::vector<base::Closure> on_load_complete_tasks_;
   size_t bytes_used_;
   size_t max_size_;
   base::TimeTicks start_time_;
   base::TimeDelta default_commit_delay_;
   RateLimiter data_rate_limiter_;
   RateLimiter commit_rate_limiter_;
   int commit_batches_in_flight_ = 0;
   std::unique_ptr<CommitBatch> commit_batch_;
   base::WeakPtrFactory<LevelDBWrapperImpl> weak_ptr_factory_;
 
   static bool s_aggressive_flushing_enabled_;
 
   DISALLOW_COPY_AND_ASSIGN(LevelDBWrapperImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_LEVELDB_WRAPPER_IMPL_H_