Implement a bag of chips for sync.

sync/engine/process_commit_response_command_unittest.cc

Index: sync/engine/process_commit_response_command_unittest.cc
diff --git a/sync/engine/process_commit_response_command_unittest.cc b/sync/engine/process_commit_response_command_unittest.cc
index 482036d7b1815e9fc6b866b2dc2a9457f6879481..2545d9ff2084616f010758f3d06c321b8f1028c3 100644
--- a/sync/engine/process_commit_response_command_unittest.cc
+++ b/sync/engine/process_commit_response_command_unittest.cc
@@ -28,6 +28,7 @@ using sync_pb::CommitResponse;
 
 namespace syncer {
 
+using sessions::StatusController;
 using sessions::SyncSession;
 using syncable::BASE_VERSION;
 using syncable::Entry;
@@ -378,6 +379,27 @@ TEST_F(ProcessCommitResponseCommandTest, NewFolderCommitKeepsChildOrder) {
       << "Too few or too many children in parent folder after commit.";
 }
 
+TEST_F(ProcessCommitResponseCommandTest, BagOfChipsPersistence) {
+  sessions::OrderedCommitSet commit_set(session()->routing_info());
+  sync_pb::ClientToServerMessage request;
+  sync_pb::ClientToServerResponse* response = const_cast<StatusController&>(
+      session()->status_controller()).mutable_updates_response();
+
+  sync_pb::ClientToServerResponse random_message;
+  random_message.set_error_message("hello");
+  random_message.set_store_birthday("world");
+  std::string serialized_message;
+  random_message.SerializeToString(&serialized_message);
+  // Bag Of Chips must be allowed to be extended by the server without the
+  // client noticing. Using a random message for it is a way to check that it is
+  // possible.
+  response->mutable_new_bag_of_chips()->ParseFromString(serialized_message);
+
+  ProcessCommitResponseCommand command(commit_set, request, *response);
+  command.ExecuteImpl(session());
+  EXPECT_EQ(serialized_message, directory()->bag_of_chips());
+}
+
 // This test fixture runs across a Cartesian product of per-type fail/success
 // possibilities.
 enum {