Limit extent of AttachContext in ContainerNode::RemoveBetween()

This patch changes extent of |AttachContext| to its lifetime for improving
code health.

Change-Id: I18b38b1a0e5f1299d8cdbf20c21608be1493a596
Reviewed-on: https://chromium-review.googlesource.com/996774Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548361}

third_party/WebKit/Source/core/dom/ContainerNode.cpp

@@ -714,10 +714,11 @@ void ContainerNode::RemoveBetween(Node* previous_child,
 
   DCHECK_EQ(old_child.parentNode(), this);
 
-  AttachContext context;
-  context.clear_invalidation = true;
-  if (!old_child.NeedsAttach())
+  if (!old_child.NeedsAttach()) {
+    AttachContext context;
+    context.clear_invalidation = true;
     old_child.DetachLayoutTree(context);
+  }
 
   if (next_child)
     next_child->SetPreviousSibling(previous_child);