Allow parent and child revisions to be modified via Conduit

Summary: See PHI1048. We have similar transactions elsewhere already (particularly, on tasks) and these edges don't have any special properties (like "Closes Txx As Wontfix" edges do) so this doesn't create any sort of peril.

Test Plan: {F6170556}

Reviewers: amckinley

Reviewed By: amckinley

Differential Revision: https://secure.phabricator.com/D20075

src/applications/differential/editor/DifferentialRevisionEditEngine.php

@@ -235,6 +235,32 @@ final class DifferentialRevisionEditEngine
       ->setConduitTypeDescription(pht('List of tasks.'))
       ->setValue(array());
 
+    $fields[] = id(new PhabricatorHandlesEditField())
+      ->setKey('parents')
+      ->setUseEdgeTransactions(true)
+      ->setIsFormField(false)
+      ->setTransactionType(PhabricatorTransactions::TYPE_EDGE)
+      ->setMetadataValue(
+        'edge:type',
+        DifferentialRevisionDependsOnRevisionEdgeType::EDGECONST)
+      ->setDescription(pht('Parent revisions of this revision.'))
+      ->setConduitDescription(pht('Change associated parent revisions.'))
+      ->setConduitTypeDescription(pht('List of revisions.'))
+      ->setValue(array());
+
+    $fields[] = id(new PhabricatorHandlesEditField())
+      ->setKey('children')
+      ->setUseEdgeTransactions(true)
+      ->setIsFormField(false)
+      ->setTransactionType(PhabricatorTransactions::TYPE_EDGE)
+      ->setMetadataValue(
+        'edge:type',
+        DifferentialRevisionDependedOnByRevisionEdgeType::EDGECONST)
+      ->setDescription(pht('Child revisions of this revision.'))
+      ->setConduitDescription(pht('Change associated child revisions.'))
+      ->setConduitTypeDescription(pht('List of revisions.'))
+      ->setValue(array());
+
     $actions = DifferentialRevisionActionTransaction::loadAllActions();
     $actions = msortv($actions, 'getRevisionActionOrderVector');