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.

third_party/blake3/BUILD.bazel

@@ -0,0 +1,49 @@
+# Description:
+# BLAKE3 is a very fast cryptographic hash function, see README.md for details.
+#
+
+licenses(["unencumbered"])  # Creative Commons CC0
+
+package(default_visibility = ["//visibility:public"])
+
+exports_files(["LICENSE"])
+
+config_setting(
+    name = "windows",
+    values = {
+        "cpu": "x64_windows",
+    },
+)
+
+cc_library(
+    name = "blake3",
+    srcs = [
+        "c/blake3.c",
+        "c/blake3_dispatch.c",
+        "c/blake3_portable.c",
+    ] + select({
+        ":windows": [
+            "c/blake3_avx2_x86-64_windows_msvc.asm",
+            "c/blake3_avx512_x86-64_windows_msvc.asm",
+            "c/blake3_sse2_x86-64_windows_msvc.asm",
+            "c/blake3_sse41_x86-64_windows_msvc.asm",
+        ],
+        "//conditions:default": [
+            "c/blake3_avx2_x86-64_unix.S",
+            "c/blake3_avx512_x86-64_unix.S",
+            "c/blake3_sse2_x86-64_unix.S",
+            "c/blake3_sse41_x86-64_unix.S",
+        ],
+    }),
+    hdrs = [
+        "c/blake3.h",
+        "c/blake3_impl.h",
+    ],
+    includes = ["c"],
+)
+
+cc_binary(
+    name = "example",
+    srcs = ["c/example.c"],
+    deps = [":blake3"],
+)