Add CIPD pin reporting to swarming.

appengine/swarming/server/task_result.py

Index: appengine/swarming/server/task_result.py
diff --git a/appengine/swarming/server/task_result.py b/appengine/swarming/server/task_result.py
index b905db0cb14a90cdc7ef7c361d44232f105af5cd..810d67a2ccee8932bfe1ec5f2154cc1d2b881505 100644
--- a/appengine/swarming/server/task_result.py
+++ b/appengine/swarming/server/task_result.py
@@ -58,6 +58,7 @@ Graph of schema:
     +---------------+  +---------------+
 """
 
+import collections
 import datetime
 import logging
 import random
@@ -373,6 +374,14 @@ class _TaskResultCommon(ndb.Model):
   # set. The isolateserver and namespace should match.
   outputs_ref = ndb.LocalStructuredProperty(task_request.FilesRef)
 
+  # The pinned versions of all the cipd packages that were specified as inputs
+  # to the task. So if the task inputs included `package/${platform}@latest`,
+  # the pinned version might be `package/windows@deadbeef`, where 'windows' is
+  # the expanded template parameter, and `deadbeef` is the resolved version of
+  # the package that the task actually used.
+  cipd_pins = ndb.LocalStructuredProperty(task_request.CipdPackage,
+                                          repeated=True)
+
   @property
   def can_be_canceled(self):
     """Returns True if the task is in a state that can be canceled."""
@@ -782,6 +791,7 @@ class TaskResultSummary(_TaskResultCommon):
 
   def reset_to_pending(self):
     """Resets this entity to pending state."""
+    self.cipd_pins = None
     self.duration = None
     self.exit_code = None
     self.internal_failure = False