Implement basic transaction detail blocks

Summary:
Some transactions (like editing configuration values, task descriptions, or Conpherence images) can't be simply explained and need an additional larger element to show them fully (like a text diff).

Support change details like this in ApplicationTransactions. Implements the element in Config, so you can see changes.

Test Plan: {F32974}

Reviewers: chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T2213

Differential Revision: https://secure.phabricator.com/D4984

src/applications/transactions/view/PhabricatorApplicationTransactionTextDiffDetailView.php

@@ -0,0 +1,45 @@
+<?php
+
+final class PhabricatorApplicationTransactionTextDiffDetailView
+  extends AphrontView {
+
+  private $oldText;
+  private $newText;
+
+  public function setNewText($new_text) {
+    $this->newText = $new_text;
+    return $this;
+  }
+
+  public function setOldText($old_text) {
+    $this->oldText = $old_text;
+    return $this;
+  }
+
+  public function render() {
+    $old = $this->oldText;
+    $new = $this->newText;
+
+    // TODO: On mobile, or perhaps by default, we should switch to 1-up once
+    // that is built.
+
+    // TODO: This should be utf8-aware, but we don't currently have a plain-text
+    // utf8 hard-wrap function. See T2554.
+    $old = wordwrap($old, 80);
+    $new = wordwrap($new, 80);
+
+    $engine = new PhabricatorDifferenceEngine();
+    $changeset = $engine->generateChangesetFromFileContent($old, $new);
+
+    $whitespace_mode = DifferentialChangesetParser::WHITESPACE_SHOW_ALL;
+
+    $parser = new DifferentialChangesetParser();
+    $parser->setChangeset($changeset);
+    $parser->setMarkupEngine(new PhabricatorMarkupEngine());
+    $parser->setWhitespaceMode($whitespace_mode);
+
+    return $parser->render(0, PHP_INT_MAX, array());
+  }
+
+}
+