Releasing the former Stadia file transfer tools

The tools allow efficient and fast synchronization of large directory
trees from a Windows workstation to a Linux target machine.

cdc_rsync* support efficient copy of files by using content-defined
chunking (CDC) to identify chunks within files that can be reused.

asset_stream_manager + cdc_fuse_fs support efficient streaming of a
local directory to a remote virtual file system based on FUSE. It also
employs CDC to identify and reuse unchanged data chunks.

data_store/data_store_writer.cc

@@ -0,0 +1,44 @@
+// Copyright 2022 Google LLC
+//
+// 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 "data_store/data_store_writer.h"
+
+#include "absl/strings/str_format.h"
+#include "common/status.h"
+#include "manifest/content_id.h"
+
+namespace cdc_ft {
+
+bool DataStoreWriter::Contains(const ContentIdProto& content_id) {
+  Buffer buffer;
+  return Get(content_id, &buffer).ok();
+}
+
+absl::Status DataStoreWriter::PutProto(
+    const google::protobuf::MessageLite& proto, ContentIdProto* content_id,
+    size_t* proto_size) {
+  // Serialize the proto.
+  std::string out;
+  if (!proto.SerializeToString(&out)) {
+    return absl::InternalError(
+        absl::StrFormat("Failed to serialize %s.", proto.GetTypeName()));
+  }
+  // Calculate the proto's content ID.
+  *content_id = ContentId::FromDataString(out);
+  if (proto_size) *proto_size = out.size();
+  // Write manifest chunk to storage.
+  return Put(*content_id, out.c_str(), out.size());
+}
+
+}  // namespace cdc_ft