Tag run-swarmed builds for later analysis

We currently have no way of tracking usage of this tool. Tagging the
builds created by it should allow us to do some basic estimation of
usage numbers.

Change-Id: Ie73a2a8019a5eb79a9b7f4e0f004b81f05251f50
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1797699Reviewed-by: Aaron Gable <agable@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Stephen Martinis <martiniss@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695760}

tools/mb/mb.py

@@ -514,6 +514,7 @@ class MetaBuildWrapper(object):
           '-I', isolate_server,
           '--namespace', namespace,
           '-S', swarming_server,
+          '--tags=purpose:user-debug-mb',
       ] + dimensions
     self._AddBaseSoftware(cmd)
     if self.args.extra_args:

tools/run-swarmed.py

@@ -52,6 +52,7 @@ def _Spawn(args):
       '-s', isolated_hash,
       '--dump-json', json_file,
       '-d', 'os', args.swarming_os,
+      '--tags=purpose:user-debug-run-swarmed',
   ]
   if args.target_os == 'fuchsia':
     trigger_args += [