Improve minor client behaviors for document rendering

Summary:
Ref T13105. This adds various small client-side improvements to document rendering.

  - In the menu, show which renderer is in use.
  - Make linking to lines work.
  - Make URIs persist information about which rendering engine is in use.
  - Improve the UI feedback for transitions between document types.
  - Load slower documents asynchronously by default.
  - Discard irrelevant requests if you spam the view menu.

Test Plan: Loaded files, linked to lines, swapped between modes, copy/pasted URLs.

Maniphest Tasks: T13105

Differential Revision: https://secure.phabricator.com/D19256

src/applications/files/document/PhabricatorDocumentEngine.php

@@ -4,6 +4,7 @@ abstract class PhabricatorDocumentEngine
   extends Phobject {
 
   private $viewer;
+  private $highlightedLines = array();
 
   final public function setViewer(PhabricatorUser $viewer) {
     $this->viewer = $viewer;
@@ -14,10 +15,23 @@ abstract class PhabricatorDocumentEngine
     return $this->viewer;
   }
 
+  final public function setHighlightedLines(array $highlighted_lines) {
+    $this->highlightedLines = $highlighted_lines;
+    return $this;
+  }
+
+  final public function getHighlightedLines() {
+    return $this->highlightedLines;
+  }
+
   final public function canRenderDocument(PhabricatorDocumentRef $ref) {
     return $this->canRenderDocumentType($ref);
   }
 
+  public function shouldRenderAsync(PhabricatorDocumentRef $ref) {
+    return false;
+  }
+
   abstract protected function canRenderDocumentType(
     PhabricatorDocumentRef $ref);
 
@@ -49,6 +63,10 @@ abstract class PhabricatorDocumentEngine
     return 'fa-file-o';
   }
 
+  protected function getDocumentRenderingText(PhabricatorDocumentRef $ref) {
+    return pht('Loading...');
+  }
+
   final public function getDocumentEngineKey() {
     return $this->getPhobjectClassConstant('ENGINEKEY');
   }
@@ -177,4 +195,20 @@ abstract class PhabricatorDocumentEngine
       $message);
   }
 
+  final public function newLoadingContent(PhabricatorDocumentRef $ref) {
+    $spinner = id(new PHUIIconView())
+      ->setIcon('fa-gear')
+      ->addClass('ph-spin');
+
+    return phutil_tag(
+      'div',
+      array(
+        'class' => 'document-engine-loading',
+      ),
+      array(
+        $spinner,
+        $this->getDocumentRenderingText($ref),
+      ));
+  }
+
 }