Calculate verity hash tree.

Calculate verity hash tree in FilesystemVerifierAction based on configs
specified in protobuf, and write it to target partition before reading
from those blocks.

A new error code kVerityCalculationError was added to report error if
it fails.

Bug: 28171891
Test: update_engine_unittests

Change-Id: I492885a0655bf51043902f578720fffd87e6a3cf
diff --git a/payload_consumer/verity_writer_stub.cc b/payload_consumer/verity_writer_stub.cc
new file mode 100644
index 0000000..a0e2467
--- /dev/null
+++ b/payload_consumer/verity_writer_stub.cc
@@ -0,0 +1,39 @@
+//
+// Copyright (C) 2018 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#include "update_engine/payload_consumer/verity_writer_stub.h"
+
+#include <memory>
+
+namespace chromeos_update_engine {
+
+namespace verity_writer {
+std::unique_ptr<VerityWriterInterface> CreateVerityWriter() {
+  return std::make_unique<VerityWriterStub>();
+}
+}  // namespace verity_writer
+
+bool VerityWriterStub::Init(const InstallPlan::Partition& partition) {
+  return partition.hash_tree_size == 0 && partition.fec_size == 0;
+}
+
+bool VerityWriterStub::Update(uint64_t offset,
+                              const uint8_t* buffer,
+                              size_t size) {
+  return true;
+}
+
+}  // namespace chromeos_update_engine