Extended the ProtoDatabase to provide LoadKeys() functionality.

components/leveldb_proto/proto_database_impl.h

Index: components/leveldb_proto/proto_database_impl.h
diff --git a/components/leveldb_proto/proto_database_impl.h b/components/leveldb_proto/proto_database_impl.h
index da02eed13876f266f1a45fc883aeae95c061039f..9997d382877a98ac3f7482c7495f20df0783e6bf 100644
--- a/components/leveldb_proto/proto_database_impl.h
+++ b/components/leveldb_proto/proto_database_impl.h
@@ -53,6 +53,8 @@ class ProtoDatabaseImpl : public ProtoDatabase<T> {
       const typename ProtoDatabase<T>::UpdateCallback& callback) override;
   void LoadEntries(
       const typename ProtoDatabase<T>::LoadCallback& callback) override;
+  void LoadKeys(
+      const typename ProtoDatabase<T>::LoadKeysCallback& callback) override;
   void GetEntry(
       const std::string& key,
       const typename ProtoDatabase<T>::GetCallback& callback) override;
@@ -94,12 +96,20 @@ void RunUpdateCallback(
 
 template <typename T>
 void RunLoadCallback(const typename ProtoDatabase<T>::LoadCallback& callback,
-                     const bool* success,
+                     bool* success,
                      std::unique_ptr<std::vector<T>> entries) {
   callback.Run(*success, std::move(entries));
 }
 
 template <typename T>
+void RunLoadKeysCallback(
+    const typename ProtoDatabase<T>::LoadKeysCallback& callback,
+    std::unique_ptr<bool> success,
+    std::unique_ptr<std::vector<std::string>> keys) {
+  callback.Run(*success, std::move(keys));
+}
+
+template <typename T>
 void RunGetCallback(const typename ProtoDatabase<T>::GetCallback& callback,
                     const bool* success,
                     const bool* found,
@@ -171,6 +181,15 @@ void LoadEntriesFromTaskRunner(LevelDB* database,
   }
 }
 
+void LoadKeysFromTaskRunner(LevelDB* database,
+                            std::vector<std::string>* keys,
+                            bool* success) {
+  DCHECK(success);
+  DCHECK(keys);
+  keys->clear();
+  *success = database->LoadKeys(keys);
+}
+
 template <typename T>
 void GetEntryFromTaskRunner(LevelDB* database,
                             const std::string& key,
@@ -286,6 +305,21 @@ void ProtoDatabaseImpl<T>::LoadEntries(
 }
 
 template <typename T>
+void ProtoDatabaseImpl<T>::LoadKeys(
+    const typename ProtoDatabase<T>::LoadKeysCallback& callback) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  auto success = base::MakeUnique<bool>(false);
+  auto keys = base::MakeUnique<std::vector<std::string>>();
+  auto load_task =
+      base::Bind(LoadKeysFromTaskRunner, base::Unretained(db_.get()),
+                 keys.get(), success.get());
+  task_runner_->PostTaskAndReply(
+      FROM_HERE, load_task,
+      base::Bind(RunLoadKeysCallback<T>, callback, base::Passed(&success),
+                 base::Passed(&keys)));
+}
+
+template <typename T>
 void ProtoDatabaseImpl<T>::GetEntry(
     const std::string& key,
     const typename ProtoDatabase<T>::GetCallback& callback) {