Added willEditTask and didEditTask for Differential.

Summary: Added constants to PhabricatorEventType. Modified DifferentialRevisionEditor and DifferentialCommentEditor.

Test Plan:
Created a revision. Edited and made a comment on that revision. It's updating as usual. I think nothing broke may be it's working.
Let me know if I have done it correclty.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin, AnhNhan

Maniphest Tasks: T2899

Differential Revision: https://secure.phabricator.com/D5869

src/applications/differential/controller/DifferentialRevisionEditController.php

@@ -56,6 +56,20 @@ final class DifferentialRevisionEditController extends DifferentialController {
       }
 
       if (!$errors) {
+        $is_new = !$revision->getID();
+        $user = $request->getUser();
+
+        $event = new PhabricatorEvent(
+          PhabricatorEventType::TYPE_DIFFERENTIAL_WILLEDITREVISION,
+            array(
+              'revision'      => $revision,
+              'new'           => $is_new,
+            ));
+
+        $event->setUser($user);
+        $event->setAphrontRequest($request);
+        PhutilEventEngine::dispatchEvent($event);
+
         $editor = new DifferentialRevisionEditor($revision);
         $editor->setActor($request->getUser());
         if ($diff) {
@@ -64,6 +78,16 @@ final class DifferentialRevisionEditController extends DifferentialController {
         $editor->setAuxiliaryFields($aux_fields);
         $editor->save();
 
+        $event = new PhabricatorEvent(
+          PhabricatorEventType::TYPE_DIFFERENTIAL_DIDEDITREVISION,
+            array(
+              'revision'      => $revision,
+              'new'           => $is_new,
+            ));
+        $event->setUser($user);
+        $event->setAphrontRequest($request);
+        PhutilEventEngine::dispatchEvent($event);
+
         return id(new AphrontRedirectResponse())
           ->setURI('/D'.$revision->getID());
       }

src/applications/differential/editor/DifferentialCommentEditor.php

@@ -492,6 +492,18 @@ final class DifferentialCommentEditor extends PhabricatorEditor {
         $actor_phid);
     }
 
+    $is_new = !$revision->getID();
+
+    $event = new PhabricatorEvent(
+      PhabricatorEventType::TYPE_DIFFERENTIAL_WILLEDITREVISION,
+        array(
+          'revision'      => $revision,
+          'new'           => $is_new,
+        ));
+
+    $event->setUser($actor);
+    PhutilEventEngine::dispatchEvent($event);
+
     $comment = id(new DifferentialComment())
       ->setAuthorPHID($actor_phid)
       ->setRevisionID($revision->getID())
@@ -546,6 +558,15 @@ final class DifferentialCommentEditor extends PhabricatorEditor {
 
         $comment->setMetadata($metadata);
         $comment->save();
+
+        $event = new PhabricatorEvent(
+          PhabricatorEventType::TYPE_DIFFERENTIAL_DIDEDITREVISION,
+            array(
+              'revision'      => $revision,
+              'new'           => $is_new,
+            ));
+        $event->setUser($actor);
+        PhutilEventEngine::dispatchEvent($event);
       }
     }
 

src/docs/userguide/events.diviner

@@ -204,6 +204,34 @@ doesn't need to be reviewed) or not.  Data available on this event:
   - ##is_generated## Boolean indicating if this file should be treated as
     generated.
 
+== Differential: Will Edit Revision ==
+
+The constant for this event is
+`PhabricatorEventType::TYPE_DIFFERENTIAL_WILLEDITREVISION`.
+
+This event is dispatched before a revision is edited, and allows you to
+respond to or alter the edit. Data available on this event:
+
+  - ##revision## The @{class:DifferentialRevision} being edited.
+  - ##new## A boolean indicating if this revision is being created.
+
+This is similar to the next event (did edit revision) but occurs before the edit
+begins.
+
+== Differential: Did Edit Revision ==
+
+The constant for this event is
+`PhabricatorEventType::TYPE_DIFFERENTIAL_DIDEDITREVISION`.
+
+This event is dispatched after a revision is edited, and allows you to
+react to the edit. Data available on this event:
+
+  - ##revision## The @{class:DifferentialRevision} being edited.
+  - ##new## A boolean indicating if this revision is being created.
+
+This is similar to the previous event (will edit revision) but occurs after the
+edit completes.
+
 == Diffusion: Did Discover Commit ==
 
 The constant for this event is
@@ -336,4 +364,4 @@ If you're having problems with your listener, try these steps:
 Continue by:
 
   - taking a look at @{class:PhabricatorExampleEventListener}; or
-  - building a library with @{article:libphutil Libraries User Guide}.
+  - building a library with @{article:libphutil Libraries User Guide}.

src/infrastructure/events/constant/PhabricatorEventType.php

@@ -15,6 +15,8 @@ final class PhabricatorEventType extends PhutilEventType {
 
   const TYPE_DIFFERENTIAL_WILLSENDMAIL      = 'differential.willSendMail';
   const TYPE_DIFFERENTIAL_WILLMARKGENERATED = 'differential.willMarkGenerated';
+  const TYPE_DIFFERENTIAL_WILLEDITREVISION  = 'differential.willEditRevision';
+  const TYPE_DIFFERENTIAL_DIDEDITREVISION   = 'differential.didEditRevision';
 
   const TYPE_DIFFUSION_DIDDISCOVERCOMMIT    = 'diffusion.didDiscoverCommit';
   const TYPE_DIFFUSION_LOOKUPUSER           = 'diffusion.lookupUser';