Attach siso metadata to the metadata, if provided.

Change-Id: I3edc6f20738fc1817aae1aaa70b63cd80d0467bd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/6544987
Reviewed-by: Fumitoshi Ukai <ukai@google.com>
Reviewed-by: Junji Watanabe <jwata@google.com>
Commit-Queue: Matt Stark <msta@google.com>

ninjalog_uploader.py

@@ -18,6 +18,7 @@ See also the privacy review. http://eldar/assessments/656778450
 
 import argparse
 import getpass
+import contextlib
 import gzip
 import http
 import io
@@ -178,6 +179,10 @@ def GetMetadata(cmdline, ninjalog, exit_code, build_duration, user):
     if jflag is not None:
         metadata["jobs"] = jflag
 
+    with contextlib.suppress(FileNotFoundError):
+        with open(os.path.join(build_dir, ".siso_metadata.json"), "r") as f:
+            metadata["siso_metadata"] = json.load(f)
+
     return metadata