Revert of Refactor frame navigation/detach state cleanup to be more sane.

Source/core/dom/Document.cpp

Index: Source/core/dom/Document.cpp
diff --git a/Source/core/dom/Document.cpp b/Source/core/dom/Document.cpp
index 83fdf6f939b7ef19b529c1958ab6bf90a4be5069..6a4f0e2b59f2e4631bfc56e442dcc7cd3e0cbe94 100644
--- a/Source/core/dom/Document.cpp
+++ b/Source/core/dom/Document.cpp
@@ -2166,19 +2166,13 @@
 
 void Document::prepareForDestruction()
 {
-    ASSERT(!m_frame || m_frame->tree().childCount() == 0);
-
+    m_markers->prepareForDestruction();
+    disconnectDescendantFrames();
+
+    // The process of disconnecting descendant frames could have already detached us.
     if (!isActive())
         return;
 
-    ScriptForbiddenScope forbidScript;
-    // We detach the FrameView's custom scroll bars as early as
-    // possible to prevent detach() from messing with the view
-    // such that its scroll bars won't be torn down.
-    //
-    // FIXME: We should revisit this.
-    view()->prepareForDetach();
-    m_markers->prepareForDestruction();
     if (LocalDOMWindow* window = this->domWindow())
         window->willDetachDocumentFromFrame();
     detach();