Add integraton test for sync backup/rollback.

sync/test/fake_server/fake_server.cc

Index: sync/test/fake_server/fake_server.cc
diff --git a/sync/test/fake_server/fake_server.cc b/sync/test/fake_server/fake_server.cc
index 25ec36ae1c38a2a4b2b4873a0557238c04fadcea..0d519e760b7c983544fdbc44b5cb2c0d3ae94c20 100644
--- a/sync/test/fake_server/fake_server.cc
+++ b/sync/test/fake_server/fake_server.cc
@@ -147,7 +147,8 @@ scoped_ptr<UpdateSieve> UpdateSieve::Create(
 
 FakeServer::FakeServer() : version_(0),
                            store_birthday_(kDefaultStoreBirthday),
-                           authenticated_(true) {
+                           authenticated_(true),
+                           error_type_(sync_pb::SyncEnums::SUCCESS) {
   keystore_keys_.push_back(kDefaultKeystoreKey);
   CHECK(CreateDefaultPermanentItems());
 }
@@ -231,6 +232,8 @@ void FakeServer::HandleCommand(const string& request,
   if (message.has_store_birthday() &&
       message.store_birthday() != store_birthday_) {
     error_code = sync_pb::SyncEnums::NOT_MY_BIRTHDAY;
+  } else if (error_type_ != sync_pb::SyncEnums::SUCCESS) {
+    error_code = error_type_;
   } else {
     bool success = false;
     switch (message.message_contents()) {
@@ -505,6 +508,15 @@ void FakeServer::SetUnauthenticated() {
   authenticated_ = false;
 }
 
+// TODO(pvalenzuela): comments from Richard: we should look at
+// mock_connection_manager.cc and take it as a warning. This style of injecting
+// errors works when there's one or two conditions we care about, but it can
+// eventually lead to a hairball once we have many different conditions and
+// triggering logic.
+void FakeServer::TriggerError(const sync_pb::SyncEnums::ErrorType& error_type) {
+  error_type_ = error_type;
+}
+
 void FakeServer::AddObserver(Observer* observer) {
   observers_.AddObserver(observer);
 }