Remove outdated FIXME.

The FIXME comment does not make sense with the current state of the
code.

Change-Id: Ia13d8de2d2b09b4bfaf5ae353c8fb439cb8e40cc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1840831
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#702837}

third_party/blink/renderer/core/dom/document.cc

@@ -2765,17 +2765,6 @@ void Document::UpdateStyleAndLayoutTree() {
 
   UpdateActiveStyle();
   UpdateStyleInvalidationIfNeeded();
-
-  // FIXME: We should update style on our ancestor chain before proceeding
-  // however doing so currently causes several tests to crash, as
-  // LocalFrame::setDocument calls Document::attach before setting the
-  // LocalDOMWindow on the LocalFrame, or the SecurityOrigin on the
-  // document. The attach, in turn resolves style (here) and then when we
-  // resolve style on the parent chain, we may end up re-attaching our
-  // containing iframe, which when asked HTMLFrameElementBase::isURLAllowed hits
-  // a null-dereference due to security code always assuming the document has a
-  // SecurityOrigin.
-
   UpdateStyle();
 
   NotifyLayoutTreeOfSubtreeChanges();