bug 1309293 - task.extra.chainOfTrust.inputs for build tasks. r=dustin

taskcluster/taskgraph/transforms/build.py

@@ -22,4 +22,8 @@ def set_defaults(config, jobs):
         if job['worker']['implementation'] in ('docker-worker', 'docker-engine'):
             job['worker'].setdefault('docker-image', {'in-tree': 'desktop-build'})
             job['worker']['chainOfTrust'] = True
+            job.setdefault('extra', {})
+            job['extra'].setdefault('chainOfTrust', {})
+            job['extra']['chainOfTrust'].setdefault('inputs', {})
+            job['extra']['chainOfTrust']['inputs']['docker-image'] = {"task-reference": "<docker-image>"}
         yield job