Update buildable containerPHIDs in a proper way via BuildWorker rather than via sneaky uncoordinated write

Summary:
Depends on D19065. Ref T13054. Instead of just updating `containerPHID` and hoping for the best, queue a proper BuildWorker to process a "your container has changed, update it" message.

We also need to remove a (superfluous) `withContainerPHIDs()` when loading active diffs for a revision.

Test Plan:
- Without daemons, created a revision and saw builds stick in "preparing" with no container PHID, but also stay in draft mode.
- With daemons, saw builds actually build and get the right container PHID.

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Maniphest Tasks: T13054

Differential Revision: https://secure.phabricator.com/D19066

src/applications/differential/editor/DifferentialTransactionEditor.php

···
         $diff->setRevisionID($object->getID());
         $diff->save();
 
-        // Update Harbormaster to set the containerPHID correctly for any
-        // existing buildables. We may otherwise have buildables stuck with
-        // the old (`null`) container.
+        // If there are any outstanding buildables for this diff, tell
+        // Harbormaster that their containers need to be updated. This is
+        // common, because `arc` creates buildables so it can upload lint
+        // and unit results.
 
-        // TODO: This is a bit iffy, maybe we can find a cleaner approach?
-        // In particular, this could (rarely) be overwritten by Harbormaster
-        // workers.
-        $table = new HarbormasterBuildable();
-        $conn_w = $table->establishConnection('w');
-        queryfx(
-          $conn_w,
-          'UPDATE %T SET containerPHID = %s WHERE buildablePHID = %s',
-          $table->getTableName(),
-          $object->getPHID(),
-          $diff->getPHID());
+        $buildables = id(new HarbormasterBuildableQuery())
+          ->setViewer(PhabricatorUser::getOmnipotentUser())
+          ->withManualBuildables(false)
+          ->withBuildablePHIDs(array($diff->getPHID()))
+          ->execute();
+        foreach ($buildables as $buildable) {
+          $buildable->sendMessage(
+            $this->getActor(),
+            HarbormasterMessageType::BUILDABLE_CONTAINER,
+            true);
+        }
 
         return;
     }

src/applications/differential/storage/DifferentialRevision.php

···
   public function loadActiveBuilds(PhabricatorUser $viewer) {
     $diff = $this->getActiveDiff();
 
+    // NOTE: We can't use `withContainerPHIDs()` here because the container
+    // update in Harbormaster is not synchronous.
     $buildables = id(new HarbormasterBuildableQuery())
       ->setViewer($viewer)
-      ->withContainerPHIDs(array($this->getPHID()))
       ->withBuildablePHIDs(array($diff->getPHID()))
       ->withManualBuildables(false)
       ->execute();

src/applications/harbormaster/engine/HarbormasterBuildEngine.php

···
       ->execute();
 
     $done_preparing = false;
+    $update_container = false;
     foreach ($messages as $message) {
       switch ($message->getType()) {
         case HarbormasterMessageType::BUILDABLE_BUILD:
           $done_preparing = true;
+          break;
+        case HarbormasterMessageType::BUILDABLE_CONTAINER:
+          $update_container = true;
           break;
         default:
           break;
···
 
     // If we received a "build" command, all builds are scheduled and we can
     // move out of "preparing" into "building".
-
     if ($done_preparing) {
       if ($buildable->isPreparing()) {
         $buildable
           ->setBuildableStatus(HarbormasterBuildableStatus::STATUS_BUILDING)
+          ->save();
+      }
+    }
+
+    // If we've been informed that the container for the buildable has
+    // changed, update it.
+    if ($update_container) {
+      $object = id(new PhabricatorObjectQuery())
+        ->setViewer($viewer)
+        ->withPHIDs(array($buildable->getBuildablePHID()))
+        ->executeOne();
+      if ($object) {
+        $buildable
+          ->setContainerPHID($object->getHarbormasterContainerPHID())
           ->save();
       }
     }

src/applications/harbormaster/engine/HarbormasterMessageType.php

···
   const MESSAGE_WORK = 'work';
 
   const BUILDABLE_BUILD = 'build';
+  const BUILDABLE_CONTAINER = 'container';
 
   public static function getAllMessages() {
     return array_keys(self::getMessageSpecifications());