Mark Owners package reviewers which own nothing in the current diff

Summary:
Ref PHI91. When Owners (or Herald, or manual user action) adds package reviewers to a revision, later updates to the revision make some of them less relevant or irrelevant.

Provide a hint when a package reviewer doesn't own any of the paths that a diff changes. Humans can then decide if the reviewer is obsolete/irrelevant or not.

This is a rough cut to get the feature working, design could probably use some tweaking if it sticks.

Test Plan: {F5204309}

Reviewers: amckinley

Reviewed By: amckinley

Subscribers: jboning

Differential Revision: https://secure.phabricator.com/D18663

src/applications/differential/controller/DifferentialRevisionViewController.php

@@ -326,11 +326,21 @@ final class DifferentialRevisionViewController extends DifferentialController {
       $other_view = $this->renderOtherRevisions($other_revisions);
     }
 
+    $this->buildPackageMaps($changesets);
+
     $toc_view = $this->buildTableOfContents(
       $changesets,
       $visible_changesets,
       $target->loadCoverageMap($viewer));
 
+    // Attach changesets to each reviewer so we can show which Owners package
+    // reviewers own no files.
+    foreach ($revision->getReviewers() as $reviewer) {
+      $reviewer_phid = $reviewer->getReviewerPHID();
+      $reviewer_changesets = $this->getPackageChangesets($reviewer_phid);
+      $reviewer->attachChangesets($reviewer_changesets);
+    }
+
     $tab_group = id(new PHUITabGroupView())
       ->addTab(
         id(new PHUITabView())