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.

common/clock.cc

@@ -0,0 +1,64 @@
+// 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 "common/clock.h"
+
+#include "absl/strings/str_format.h"
+#include "common/platform.h"
+
+namespace cdc_ft {
+
+// static
+DefaultSteadyClock* DefaultSteadyClock::GetInstance() {
+  static DefaultSteadyClock instance;
+  return &instance;
+}
+
+SteadyClock::Timestamp DefaultSteadyClock::Now() const {
+  return std::chrono::steady_clock::now();
+}
+
+std::string SystemClock::FormatNow(const char* format,
+                                   bool append_millis) const {
+  const Timestamp now = Now();
+  const std::time_t now_t = std::chrono::system_clock::to_time_t(now);
+  tm now_tm;
+#if PLATFORM_WINDOWS
+  localtime_s(&now_tm, &now_t);
+#elif PLATFORM_LINUX
+  localtime_r(&now_t, &now_tm);
+#endif
+  std::stringstream ss;
+  ss << std::put_time(&now_tm, format);
+
+  if (append_millis) {
+    const int millis = std::chrono::duration_cast<std::chrono::milliseconds>(
+                           now - std::chrono::system_clock::from_time_t(now_t))
+                           .count();
+    ss << std::setfill('0') << std::setw(3) << millis;
+  }
+  return ss.str();
+}
+
+// static
+DefaultSystemClock* DefaultSystemClock::GetInstance() {
+  static DefaultSystemClock instance;
+  return &instance;
+}
+
+SystemClock::Timestamp DefaultSystemClock::Now() const {
+  return std::chrono::system_clock::now();
+}
+
+}  // namespace cdc_ft