Bug 1458556: Release wallpaper for bug 1462401. r=xidorn

Just avoid crashing if the element has no data, treat is as display: none.

TakeChangeHint already returns wasRestyled = false, so we won't end up trying to
reconstruct anything, and we don't set frame construction flags in
nsCSSFrameConstructor so we won't traverse children either.

MozReview-Commit-ID: 2gXmHSlj3Jw

--HG--
extra : rebase_source : 9d95a4f3ee8fabc4d73a39699c677ba184061370

layout/base/RestyleManager.cpp

@@ -2671,7 +2671,8 @@ RestyleManager::ProcessPostTraversal(
              "display: contents node has a frame, yet we didn't reframe it"
              " above?");
   const bool isDisplayContents =
-    !styleFrame && Servo_Element_IsDisplayContents(aElement);
+    !styleFrame && aElement->HasServoData() &&
+    Servo_Element_IsDisplayContents(aElement);
   if (isDisplayContents) {
     oldOrDisplayContentsStyle =
       aRestyleState.StyleSet().ResolveServoStyle(aElement);