Display full picture in image macro editing

Summary:
Users are complaining that they don't see how the image macro looks until they use it.
Click leads to edit form.
Display it there.

Test Plan:
Edited macro.
Attempted to create macro with duplicate name.

Reviewers: epriestley

Reviewed By: epriestley

CC: chad, aran, Korvin

Differential Revision: https://secure.phabricator.com/D3636

src/applications/macro/controller/PhabricatorMacroEditController.php

@@ -38,6 +38,7 @@ final class PhabricatorMacroEditController
 
     $errors = array();
     $e_name = true;
+    $file = null;
 
     $request = $this->getRequest();
     $user = $request->getUser();
@@ -75,6 +76,18 @@ final class PhabricatorMacroEditController
           $e_name = 'Duplicate';
         }
       }
+    } else if ($this->id) {
+      $file = id(new PhabricatorFile())
+        ->loadOneWhere('phid = %s', $macro->getFilePHID());
+    }
+
+    $caption = null;
+    if ($file) {
+      $caption = phutil_render_tag(
+        'img',
+        array(
+          'src' => $file->getViewURI(),
+        ));
     }
 
     if ($errors) {
@@ -102,6 +115,7 @@ final class PhabricatorMacroEditController
         id(new AphrontFormFileControl())
           ->setLabel('File')
           ->setName('file')
+          ->setCaption($caption)
           ->setError(true))
       ->appendChild(
         id(new AphrontFormSubmitControl())