Make AuthProvider, ExternalAccount, and ExternalAccountIdentifier all Destructible

Summary: Depends on D21014. Ref T13493. Make these objects all use destructible interfaces and destroy sub-objects appropriately.

Test Plan:
- Used `bin/remove destroy --trace ...` to destroy a provider, a user, and an external account.
- Observed destruction of sub-objects, including external account identifiers.

Maniphest Tasks: T13493

Differential Revision: https://secure.phabricator.com/D21015

src/__phutil_library_map__.php

···
       'PhabricatorAuthDAO',
       'PhabricatorApplicationTransactionInterface',
       'PhabricatorPolicyInterface',
+      'PhabricatorDestructibleInterface',
     ),
     'PhabricatorAuthProviderConfigController' => 'PhabricatorAuthProviderController',
     'PhabricatorAuthProviderConfigEditor' => 'PhabricatorApplicationTransactionEditor',
···
     'PhabricatorExternalAccount' => array(
       'PhabricatorUserDAO',
       'PhabricatorPolicyInterface',
+      'PhabricatorDestructibleInterface',
     ),
     'PhabricatorExternalAccountIdentifier' => array(
       'PhabricatorUserDAO',
       'PhabricatorPolicyInterface',
+      'PhabricatorDestructibleInterface',
     ),
     'PhabricatorExternalAccountIdentifierQuery' => 'PhabricatorCursorPagedPolicyAwareQuery',
     'PhabricatorExternalAccountQuery' => 'PhabricatorCursorPagedPolicyAwareQuery',

src/applications/auth/storage/PhabricatorAuthProviderConfig.php

···
   extends PhabricatorAuthDAO
   implements
     PhabricatorApplicationTransactionInterface,
-    PhabricatorPolicyInterface {
+    PhabricatorPolicyInterface,
+    PhabricatorDestructibleInterface {
 
   protected $providerClass;
   protected $providerType;
···
 
   public function hasAutomaticCapability($capability, PhabricatorUser $viewer) {
     return false;
+  }
+
+
+/* -(  PhabricatorDestructibleInterface  )----------------------------------- */
+
+
+  public function destroyObjectPermanently(
+    PhabricatorDestructionEngine $engine) {
+
+    $viewer = $engine->getViewer();
+    $config_phid = $this->getPHID();
+
+    $accounts = id(new PhabricatorExternalAccountQuery())
+      ->setViewer($viewer)
+      ->withProviderConfigPHIDs(array($config_phid))
+      ->newIterator();
+    foreach ($accounts as $account) {
+      $engine->destroyObject($account);
+    }
+
+    $identifiers = id(new PhabricatorExternalAccountIdentifierQuery())
+      ->setViewer($viewer)
+      ->withProviderConfigPHIDs(array($config_phid))
+      ->newIterator();
+    foreach ($identifiers as $identifier) {
+      $engine->destroyObject($identifier);
+    }
+
+    $this->delete();
   }
 
 }

src/applications/people/storage/PhabricatorExternalAccount.php

···
 <?php
 
-final class PhabricatorExternalAccount extends PhabricatorUserDAO
-  implements PhabricatorPolicyInterface {
+final class PhabricatorExternalAccount
+  extends PhabricatorUserDAO
+  implements
+    PhabricatorPolicyInterface,
+    PhabricatorDestructibleInterface {
 
   protected $userPHID;
   protected $accountType;
···
         return pht(
           'External accounts can only be edited by the account owner.');
     }
+  }
+
+
+/* -(  PhabricatorDestructibleInterface  )----------------------------------- */
+
+
+  public function destroyObjectPermanently(
+    PhabricatorDestructionEngine $engine) {
+
+    $viewer = $engine->getViewer();
+
+    $identifiers = id(new PhabricatorExternalAccountIdentifierQuery())
+      ->setViewer($viewer)
+      ->withExternalAccountPHIDs(array($this->getPHID()))
+      ->newIterator();
+    foreach ($identifiers as $identifier) {
+      $engine->destroyObject($identifier);
+    }
+
+    $this->delete();
   }
 
 }

src/applications/people/storage/PhabricatorExternalAccountIdentifier.php

···
 
 final class PhabricatorExternalAccountIdentifier
   extends PhabricatorUserDAO
-  implements PhabricatorPolicyInterface {
+  implements
+    PhabricatorPolicyInterface,
+    PhabricatorDestructibleInterface {
 
   protected $externalAccountPHID;
   protected $providerConfigPHID;
···
 
   public function hasAutomaticCapability($capability, PhabricatorUser $viewer) {
     return false;
+  }
+
+
+/* -(  PhabricatorDestructibleInterface  )----------------------------------- */
+
+
+  public function destroyObjectPermanently(
+    PhabricatorDestructionEngine $engine) {
+    $this->delete();
   }
 
 }

src/applications/people/storage/PhabricatorUser.php

···
   public function destroyObjectPermanently(
     PhabricatorDestructionEngine $engine) {
 
+    $viewer = $engine->getViewer();
+
     $this->openTransaction();
       $this->delete();
 
       $externals = id(new PhabricatorExternalAccountQuery())
-        ->setViewer($engine->getViewer())
+        ->setViewer($viewer)
         ->withUserPHIDs(array($this->getPHID()))
-        ->execute();
+        ->newIterator();
       foreach ($externals as $external) {
-        $external->delete();
+        $engine->destroyObject($external);
       }
 
       $prefs = id(new PhabricatorUserPreferencesQuery())
-        ->setViewer($engine->getViewer())
+        ->setViewer($viewer)
         ->withUsers(array($this))
         ->execute();
       foreach ($prefs as $pref) {
···
       }
 
       $keys = id(new PhabricatorAuthSSHKeyQuery())
-        ->setViewer($engine->getViewer())
+        ->setViewer($viewer)
         ->withObjectPHIDs(array($this->getPHID()))
         ->execute();
       foreach ($keys as $key) {

src/infrastructure/query/policy/PhabricatorCursorPagedPolicyAwareQuery.php

···
     return $results;
   }
 
+  final public function newIterator() {
+    return new PhabricatorQueryIterator($this);
+  }
+
   final public function executeWithCursorPager(AphrontCursorPagerView $pager) {
     $limit = $pager->getPageSize();