sync: Add non-blocking type encryption (retry)

sync/test/engine/mock_model_type_sync_worker.h

Index: sync/test/engine/mock_model_type_sync_worker.h
diff --git a/sync/test/engine/mock_model_type_sync_worker.h b/sync/test/engine/mock_model_type_sync_worker.h
index 498e9ee080c8893efe32a441b962d8b547c421ca..b33e548b7bd40a76553350a1670abac31fc31a1a 100644
--- a/sync/test/engine/mock_model_type_sync_worker.h
+++ b/sync/test/engine/mock_model_type_sync_worker.h
@@ -57,6 +57,11 @@ class MockModelTypeSyncWorker : public ModelTypeSyncWorker {
   CommitResponseData SuccessfulCommitResponse(
       const CommitRequestData& request_data);
 
+  // Sets the encryption key name used for updates from the server.
+  // (ie. the key other clients are using to encrypt their commits.)
+  // The default value is an empty string, which indicates no encryption.
+  void SetServerEncryptionKey(const std::string& key_name);
+
  private:
   // Generate an ID string.
   static std::string GenerateId(const std::string& tag_hash);
@@ -72,6 +77,9 @@ class MockModelTypeSyncWorker : public ModelTypeSyncWorker {
   // This is an essential part of the mocked server state.
   std::map<const std::string, int64> server_versions_;
 
+  // Name of the encryption key in use on other clients.
+  std::string server_encryption_key_name_;
+
   DISALLOW_COPY_AND_ASSIGN(MockModelTypeSyncWorker);
 };