[sync] Reland - Replace FakeServer's implementation with LoopbackServer invocations.

components/sync/engine_impl/loopback_server/persistent_unique_client_entity.cc

Index: components/sync/engine_impl/loopback_server/persistent_unique_client_entity.cc
diff --git a/components/sync/engine_impl/loopback_server/persistent_unique_client_entity.cc b/components/sync/engine_impl/loopback_server/persistent_unique_client_entity.cc
index 9a2b8725b17d1d4c877cc6e15c0a33f6ad4df74e..2554ab6a39b7b448c9b51e793274bd0b9e7e21ae 100644
--- a/components/sync/engine_impl/loopback_server/persistent_unique_client_entity.cc
+++ b/components/sync/engine_impl/loopback_server/persistent_unique_client_entity.cc
@@ -5,6 +5,7 @@
 #include "components/sync/engine_impl/loopback_server/persistent_unique_client_entity.h"
 
 #include "base/guid.h"
+#include "components/sync/base/hash_util.h"
 #include "components/sync/engine_impl/loopback_server/persistent_permanent_entity.h"
 #include "components/sync/protocol/sync.pb.h"
 
@@ -31,7 +32,8 @@ PersistentUniqueClientEntity::PersistentUniqueClientEntity(
 PersistentUniqueClientEntity::~PersistentUniqueClientEntity() {}
 
 // static
-std::unique_ptr<LoopbackServerEntity> PersistentUniqueClientEntity::Create(
+std::unique_ptr<LoopbackServerEntity>
+PersistentUniqueClientEntity::CreateFromEntity(
     const sync_pb::SyncEntity& client_entity) {
   CHECK(client_entity.has_client_defined_unique_tag())
       << "A PersistentUniqueClientEntity must have a client-defined unique "
@@ -45,6 +47,20 @@ std::unique_ptr<LoopbackServerEntity> PersistentUniqueClientEntity::Create(
 }
 
 // static
+std::unique_ptr<LoopbackServerEntity>
+PersistentUniqueClientEntity::CreateFromEntitySpecifics(
+    const string& name,
+    const sync_pb::EntitySpecifics& entity_specifics) {
+  ModelType model_type = GetModelTypeFromSpecifics(entity_specifics);
+  string client_defined_unique_tag = GenerateSyncableHash(model_type, name);
+  string id =
+      LoopbackServerEntity::CreateId(model_type, client_defined_unique_tag);
+  return std::unique_ptr<LoopbackServerEntity>(new PersistentUniqueClientEntity(
+      id, model_type, 0, name, client_defined_unique_tag, entity_specifics,
+      1337, 1337));
+}
+
+// static
 std::string PersistentUniqueClientEntity::EffectiveIdForClientTaggedEntity(
     const sync_pb::SyncEntity& entity) {
   return LoopbackServerEntity::CreateId(