[Squad] Recalculate style separately for AttachContext tests.

We relied on LayoutTreeBuilderForElement to compute style through
StyleForLayoutObject for these tests. Compute style in style recalc pass
as we would do in production.

Bug: 843520
Change-Id: Ib03317c479f06f3aecad668a8bdba0924fa5b8f5
Reviewed-on: https://chromium-review.googlesource.com/1065683Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#560364}

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

@@ -40,7 +40,9 @@ class NodeTest : public EditingTestBase {
   }
 
   LayoutObject* ReattachLayoutTreeForNode(Node& node) {
+    node.LazyReattachIfAttached();
     GetDocument().Lifecycle().AdvanceTo(DocumentLifecycle::kInStyleRecalc);
+    GetDocument().documentElement()->RecalcStyle(kNoChange);
     PushSelectorFilterAncestors(
         GetDocument().EnsureStyleResolver().GetSelectorFilter(), node);
     Node::AttachContext context;