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/stats_collector.h

@@ -0,0 +1,54 @@
+/*
+ * 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.
+ */
+
+#ifndef COMMON_STATS_COLLECTOR_H_
+#define COMMON_STATS_COLLECTOR_H_
+
+#include <memory>
+
+namespace cdc_ft {
+
+class StatsCollector {
+ public:
+  StatsCollector();
+  virtual ~StatsCollector();
+
+  // Initializes the stats collector. If not called, the instance returned from
+  // Instance() is a no-op stats collector where all calls have no effect.
+  static void Initialize();
+
+  // Shuts down the stats collector. Should be called during shutdown if
+  // Initialize() was called during startup.
+  static void Shutdown();
+
+  // Returns a no-op stats collector if Initialize() has not been called.
+  static StatsCollector* Instance();
+
+  class DurationScope {
+   public:
+    virtual ~DurationScope();
+  };
+
+  virtual void IncCounter(const char* name, size_t value = 1) = 0;
+  virtual std::unique_ptr<DurationScope> RecordDuration(const char* name) = 0;
+
+ private:
+  static StatsCollector* instance_;
+};
+
+}  // namespace cdc_ft
+
+#endif  // COMMON_STATS_COLLECTOR_H_