Adjust code to look for the HTML element, not the document

This was a mistake in the previous patch. When walking up the DOM tree,
we don't encounter the document object directly (this is different than
the layout tree).

Bug: 1129979

Change-Id: Ib6b7040e2a54658948d0830230d7a8ebeba44b8f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2446517Reviewed-by: Scott Little <sclittle@chromium.org>
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813389}

third_party/blink/renderer/core/html/lazy_load_image_observer.cc

@@ -84,12 +84,11 @@ bool IsElementInInvisibleSubTree(const Element& element) {
     return true;
   for (Node& ancestor : FlatTreeTraversal::InclusiveAncestorsOf(element)) {
     auto* ancestor_element = DynamicTo<Element>(ancestor);
-    if (!ancestor_element) {
-      // Return true if the whole frame is not rendered.
-      if (ancestor.IsDocumentNode() && !ancestor.GetLayoutObject())
-        return true;
+    if (!ancestor_element)
       continue;
-    }
+    // Return true if the whole frame is not rendered.
+    if (ancestor.IsHTMLElement() && !ancestor.GetLayoutObject())
+      return true;
     const ComputedStyle* style = ancestor_element->EnsureComputedStyle();
     if (style && (style->Visibility() != EVisibility::kVisible ||
                   style->Display() == EDisplay::kNone)) {