Add a basic push log for recording repository push events

Summary:
Ref T4195. This log serves two purposes:

  - It's a log, so you can see what happened. Particularly, in Git/Hg, there is no other way to tell:
    - Who //pushed// a change (vs committed / authored)?
    - When was a change pushed?
    - What was the old value of some tag/branch before someone destroyed it?
  - We can hand these objects off to Herald to implement pre-commit rules.

This is a very basic implementation, but gets some data written and has a basic UI for it.

Test Plan: {F87339}

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T4195

Differential Revision: https://secure.phabricator.com/D7705

src/applications/repository/query/PhabricatorRepositoryPushLogSearchEngine.php

@@ -0,0 +1,49 @@
+<?php
+
+final class PhabricatorRepositoryPushLogSearchEngine
+  extends PhabricatorApplicationSearchEngine {
+
+  public function buildSavedQueryFromRequest(AphrontRequest $request) {
+    $saved = new PhabricatorSavedQuery();
+
+    return $saved;
+  }
+
+  public function buildQueryFromSavedQuery(PhabricatorSavedQuery $saved) {
+    $query = id(new PhabricatorRepositoryPushLogQuery());
+
+    return $query;
+  }
+
+  public function buildSearchForm(
+    AphrontFormView $form,
+    PhabricatorSavedQuery $saved_query) {
+
+  }
+
+  protected function getURI($path) {
+    return '/diffusion/pushlog/'.$path;
+  }
+
+  public function getBuiltinQueryNames() {
+    $names = array(
+      'all' => pht('All Push Logs'),
+    );
+
+    return $names;
+  }
+
+  public function buildSavedQueryFromBuiltin($query_key) {
+
+    $query = $this->newSavedQuery();
+    $query->setQueryKey($query_key);
+
+    switch ($query_key) {
+      case 'all':
+        return $query;
+    }
+
+    return parent::buildSavedQueryFromBuiltin($query_key);
+  }
+
+}