Use correct cascading order for Shadow DOM v1

third_party/WebKit/Source/core/dom/StyleEngine.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
@@ skipping 159 matching lines @@
     void attributeChangedForElement(const QualifiedName& attributeName, Element&);
     void idChangedForElement(const AtomicString& oldId, const AtomicString& newId, Element&);
     void pseudoStateChangedForElement(CSSSelector::PseudoType, Element&);
 
     unsigned styleForElementCount() const { return m_styleForElementCount; }
     void incStyleForElementCount() { m_styleForElementCount++; }
 
     StyleResolverStats* stats() { return m_styleResolverStats.get(); }
     void setStatsEnabled(bool);
 
+    bool useCascadeOrderForShadowDOMV1() const { return m_useCascadeOrderForShadowDOMV1; }
+    void setUseCascadeOrderForShadowDOMV1() { m_useCascadeOrderForShadowDOMV1 = true; }

[rune, 2016/03/18 12:04:12]

We are not recalculating style setting this flag, so currently we may end up
with different elements using different cascading order, but will gradually
change style as their style is invalidated for different mutations.

Attaching one v1 shadow will forever make this document use the v1 cascading
order, which is probably fine.

If you want to have consistent cascading across the document, you could have a
cascade order enum { SHADOW_CASCADE_NONE, SHADOW_CASCADE_V0, SHADOW_CASCADE_V1
}, start at SHADOW_CASCADE_NONE, always increase, and mark the whole document
for style recalc when changing from SHADOW_CASCADE_V0 to SHADOW_CASCADE_V1.

[kochi, 2016/03/22 08:16:59]

Very good point.
I've added the enum and set style recalc flag on V0->V1 upgrade timing.
Also added a test for the case.

+
     DECLARE_VIRTUAL_TRACE();
 
 private:
     // CSSFontSelectorClient implementation.
     void fontsNeedUpdate(CSSFontSelector*) override;
 
 private:
     StyleEngine(Document&);
 
     TreeScopeStyleSheetCollection* ensureStyleSheetCollectionFor(TreeScope&);
@@ skipping 54 matching lines @@
     String m_selectedStylesheetSetName;
 
     bool m_usesSiblingRules = false;
     bool m_usesFirstLineRules = false;
     bool m_usesWindowInactiveSelector = false;
     bool m_usesRemUnits = false;
     unsigned m_maxDirectAdjacentSelectors = 0;
 
     bool m_ignorePendingStylesheets = false;
     bool m_didCalculateResolver = false;
+
+    bool m_useCascadeOrderForShadowDOMV1 = false;
+
     OwnPtrWillBeMember<StyleResolver> m_resolver;
     StyleInvalidator m_styleInvalidator;
 
     RefPtrWillBeMember<CSSFontSelector> m_fontSelector;
 
     WillBeHeapHashMap<AtomicString, RawPtrWillBeMember<StyleSheetContents>> m_textToSheetCache;
     WillBeHeapHashMap<RawPtrWillBeMember<StyleSheetContents>, AtomicString> m_sheetToTextCache;
 
     OwnPtr<StyleResolverStats> m_styleResolverStats;
     unsigned m_styleForElementCount = 0;
 
     friend class StyleEngineTest;
 };
 
 } // namespace blink
 
 #endif