Improve UX for repository updates

Summary:
Fixes T5926. Fixes T5830. Ref T4767. Users currently sometimes have a hard time understanding repository update frequencies. This is compounded by aggressive backoff and incorrect backoff while importing repositories.

  - Don't back off while importing repositories. This prevents us from hanging at 99.99% for inactive repositories while waiting for the next update.
  - Back off less aggressively in general, and even more gradually during the first 3 days. This should make behavior around weekends better.
  - Show update frequency in the UI.
  - Provide an explicit "update now" button to call `diffusion.looksoon` in a more user-friendly way.
  - Document how backoff policies work and how to adjust behavior.

Test Plan:
  - Ran `bin/phd debug pulllocal` and verified backoff worked correctly from debugging output.
  - Clicked "Update Now" to get a hint, reloaded page to see it update.
  - Read documentation.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4767, T5830, T5926

Differential Revision: https://secure.phabricator.com/D10323

src/applications/diffusion/controller/DiffusionRepositoryEditUpdateController.php

@@ -0,0 +1,75 @@
+<?php
+
+final class DiffusionRepositoryEditUpdateController
+  extends DiffusionRepositoryEditController {
+
+  public function processRequest() {
+    $request = $this->getRequest();
+    $viewer = $request->getUser();
+    $drequest = $this->diffusionRequest;
+    $repository = $drequest->getRepository();
+
+    $repository = id(new PhabricatorRepositoryQuery())
+      ->setViewer($viewer)
+      ->requireCapabilities(
+        array(
+          PhabricatorPolicyCapability::CAN_VIEW,
+          PhabricatorPolicyCapability::CAN_EDIT,
+        ))
+      ->withIDs(array($repository->getID()))
+      ->executeOne();
+    if (!$repository) {
+      return new Aphront404Response();
+    }
+
+    $edit_uri = $this->getRepositoryControllerURI($repository, 'edit/');
+
+    if ($request->isFormPost()) {
+      $params = array(
+        'callsigns' => array(
+          $repository->getCallsign(),
+        ),
+      );
+
+      id(new ConduitCall('diffusion.looksoon', $params))
+        ->setUser($viewer)
+        ->execute();
+
+      return id(new AphrontRedirectResponse())->setURI($edit_uri);
+    }
+
+    $doc_name = 'Diffusion User Guide: Repository Updates';
+    $doc_href = PhabricatorEnv::getDoclink($doc_name);
+    $doc_link = phutil_tag(
+      'a',
+      array(
+        'href' => $doc_href,
+        'target' => '_blank',
+      ),
+      $doc_name);
+
+    return $this->newDialog()
+      ->setTitle(pht('Update Repository Now'))
+      ->appendParagraph(
+        pht(
+          'Normally, Phabricator automatically updates repositories '.
+          'based on how much time has elapsed since the last commit. '.
+          'This helps reduce load if you have a large number of mostly '.
+          'inactive repositories, which is common.'))
+      ->appendParagraph(
+        pht(
+          'You can manually schedule an update for this repository. The '.
+          'daemons will perform the update as soon as possible. This may '.
+          'be helpful if you have just made a commit to a rarely used '.
+          'repository.'))
+      ->appendParagraph(
+        pht(
+          'To learn more about how Phabricator updates repositories, '.
+          'read %s in the documentation.',
+          $doc_link))
+      ->addCancelButton($edit_uri)
+      ->addSubmitButton(pht('Schedule Update'));
+  }
+
+
+}