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_android.h b/payload_consumer/verity_writer_android.h
new file mode 100644
index 0000000..c26663b
--- /dev/null
+++ b/payload_consumer/verity_writer_android.h
@@ -0,0 +1,46 @@
+//
+// 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.
+//
+
+#ifndef UPDATE_ENGINE_PAYLOAD_CONSUMER_VERITY_WRITER_ANDROID_H_
+#define UPDATE_ENGINE_PAYLOAD_CONSUMER_VERITY_WRITER_ANDROID_H_
+
+#include <memory>
+
+#include <verity/hash_tree_builder.h>
+
+#include "update_engine/payload_consumer/verity_writer_interface.h"
+
+namespace chromeos_update_engine {
+
+class VerityWriterAndroid : public VerityWriterInterface {
+ public:
+  VerityWriterAndroid() = default;
+  ~VerityWriterAndroid() override = default;
+
+  bool Init(const InstallPlan::Partition& partition) override;
+  bool Update(uint64_t offset, const uint8_t* buffer, size_t size) override;
+
+ private:
+  const InstallPlan::Partition* partition_ = nullptr;
+
+  std::unique_ptr<HashTreeBuilder> hash_tree_builder_;
+
+  DISALLOW_COPY_AND_ASSIGN(VerityWriterAndroid);
+};
+
+}  // namespace chromeos_update_engine
+
+#endif  // UPDATE_ENGINE_PAYLOAD_CONSUMER_VERITY_WRITER_ANDROID_H_