Make SkyShell stop crashing on scroll in Stocks2.

sky/engine/core/painting/LayoutRoot.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sky/engine/config.h"
 #include "sky/engine/core/painting/LayoutRoot.h"
 
 #include "sky/engine/core/dom/Document.h"
 #include "sky/engine/core/dom/Element.h"
 #include "sky/engine/core/frame/FrameView.h"
@@ skipping 19 matching lines @@
     m_settings = Settings::create();
     m_settings->setDefaultFixedFontSize(13);
     m_settings->setDefaultFontSize(16);
     m_frameHost = FrameHost::createDummy(m_settings.get());
     m_frame = LocalFrame::create(nullptr, m_frameHost.get());
     m_frame->createView(IntSize(), Color::white, false);
 }
 
 LayoutRoot::~LayoutRoot()
 {
+    if (!m_document->needsAttach())
+        m_document->detach();
 }
 
 Element* LayoutRoot::rootElement() const
 {
     if (!m_document)
         return nullptr;
     return m_document->firstElementChild();
 }
 
 void LayoutRoot::setRootElement(Element* root)
@@ skipping 27 matching lines @@
     m_frame->setDocument(nullptr);
 }
 
 void LayoutRoot::paint(Canvas* canvas)
 {
     if (m_document)
         rootElement()->paint(canvas);
 }
 
 } // namespace blink