Extended the ProtoDatabase to provide LoadKeys() functionality.

components/leveldb_proto/testing/fake_db.h

Index: components/leveldb_proto/testing/fake_db.h
diff --git a/components/leveldb_proto/testing/fake_db.h b/components/leveldb_proto/testing/fake_db.h
index e67ceba7a8ccc238a4af9027b91725ac297c2ac5..bd9efb571a465f4e3b05d4b98e63d073d3ca6498 100644
--- a/components/leveldb_proto/testing/fake_db.h
+++ b/components/leveldb_proto/testing/fake_db.h
@@ -39,6 +39,8 @@ class FakeDB : 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;
@@ -51,6 +53,8 @@ class FakeDB : public ProtoDatabase<T> {
 
   void LoadCallback(bool success);
 
+  void LoadKeysCallback(bool success);
+
   void GetCallback(bool success);
 
   void UpdateCallback(bool success);
@@ -63,6 +67,11 @@ class FakeDB : public ProtoDatabase<T> {
       std::unique_ptr<typename std::vector<T>> entries,
       bool success);
 
+  static void RunLoadKeysCallback(
+      const typename ProtoDatabase<T>::LoadKeysCallback& callback,
+      std::unique_ptr<std::vector<std::string>> keys,
+      bool success);
+
   static void RunGetCallback(
       const typename ProtoDatabase<T>::GetCallback& callback,
       std::unique_ptr<T> entry,
@@ -73,6 +82,7 @@ class FakeDB : public ProtoDatabase<T> {
 
   Callback init_callback_;
   Callback load_callback_;
+  Callback load_keys_callback_;
   Callback get_callback_;
   Callback update_callback_;
 };
@@ -118,6 +128,18 @@ void FakeDB<T>::LoadEntries(
 }
 
 template <typename T>
+void FakeDB<T>::LoadKeys(
+    const typename ProtoDatabase<T>::LoadKeysCallback& callback) {
+  std::unique_ptr<std::vector<std::string>> keys(
+      new std::vector<std::string>());
+  for (const auto& pair : *db_)
+    keys->push_back(pair.first);
+
+  load_keys_callback_ =
+      base::Bind(RunLoadKeysCallback, callback, base::Passed(&keys));
+}
+
+template <typename T>
 void FakeDB<T>::GetEntry(
     const std::string& key,
     const typename ProtoDatabase<T>::GetCallback& callback) {
@@ -152,6 +174,12 @@ void FakeDB<T>::LoadCallback(bool success) {
 }
 
 template <typename T>
+void FakeDB<T>::LoadKeysCallback(bool success) {
+  load_keys_callback_.Run(success);
+  load_keys_callback_.Reset();
+}
+
+template <typename T>
 void FakeDB<T>::GetCallback(bool success) {
   get_callback_.Run(success);
   get_callback_.Reset();
@@ -174,6 +202,15 @@ void FakeDB<T>::RunLoadCallback(
 
 // static
 template <typename T>
+void FakeDB<T>::RunLoadKeysCallback(
+    const typename ProtoDatabase<T>::LoadKeysCallback& callback,
+    std::unique_ptr<std::vector<std::string>> keys,
+    bool success) {
+  callback.Run(success, std::move(keys));
+}
+
+// static
+template <typename T>
 void FakeDB<T>::RunGetCallback(
     const typename ProtoDatabase<T>::GetCallback& callback,
     std::unique_ptr<T> entry,