When creating a File storage object for a Paste, try to give it the same name as the Paste

Summary:
Ref T13528. Paste data is stored in files, but the files are always named "raw.txt".

Now that Paste provides a hint to use Files for "DocumentEngine" rendering, try to use the same name as the paste instead.

Test Plan:
  - Created a paste named "staggering-insight.ipynb".
  - Clicked "View as Jupyter Notebook" from Paste.
  - Saw a file named "staggering-insight.ipynb", not "raw.txt".
  - Created a paste with no name, saw a file named "raw-paste-data.txt" get created.

Maniphest Tasks: T13528

Differential Revision: https://secure.phabricator.com/D21197

src/applications/paste/editor/PhabricatorPasteEditor.php

@@ -3,6 +3,12 @@
 final class PhabricatorPasteEditor
   extends PhabricatorApplicationTransactionEditor {
 
+  private $newPasteTitle;
+
+  public function getNewPasteTitle() {
+    return $this->newPasteTitle;
+  }
+
   public function getEditorApplicationClass() {
     return 'PhabricatorPasteApplication';
   }
@@ -29,6 +35,22 @@ final class PhabricatorPasteEditor
     return $types;
   }
 
+  protected function expandTransactions(
+    PhabricatorLiskDAO $object,
+    array $xactions) {
+
+    $new_title = $object->getTitle();
+    foreach ($xactions as $xaction) {
+      $type = $xaction->getTransactionType();
+      if ($type === PhabricatorPasteTitleTransaction::TRANSACTIONTYPE) {
+        $new_title = $xaction->getNewValue();
+      }
+    }
+    $this->newPasteTitle = $new_title;
+
+    return parent::expandTransactions($object, $xactions);
+  }
+
   protected function shouldSendMail(
     PhabricatorLiskDAO $object,
     array $xactions) {

src/applications/paste/xaction/PhabricatorPasteContentTransaction.php

@@ -50,10 +50,17 @@ final class PhabricatorPasteContentTransaction
   }
 
   private function newFileForPaste(PhabricatorUser $actor, $data) {
+    $editor = $this->getEditor();
+
+    $file_name = $editor->getNewPasteTitle();
+    if (!strlen($file_name)) {
+      $file_name = 'raw-paste-data.txt';
+    }
+
     return PhabricatorFile::newFromFileData(
       $data,
       array(
-        'name' => 'raw.txt',
+        'name' => $file_name,
         'mime-type' => 'text/plain; charset=utf-8',
         'authorPHID' => $actor->getPHID(),
         'viewPolicy' => PhabricatorPolicies::POLICY_NOONE,