Use correct cascading order for Shadow DOM v1

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

Index: third_party/WebKit/Source/core/dom/StyleEngine.h
diff --git a/third_party/WebKit/Source/core/dom/StyleEngine.h b/third_party/WebKit/Source/core/dom/StyleEngine.h
index b44b36431bc352be722f4f4a9a2bd0b7447953e5..5dff0e4339ed1f68d0c174ac594353ca62e2209c 100644
--- a/third_party/WebKit/Source/core/dom/StyleEngine.h
+++ b/third_party/WebKit/Source/core/dom/StyleEngine.h
@@ -177,6 +177,9 @@ public:
     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:
@@ -251,6 +254,9 @@ private:
 
     bool m_ignorePendingStylesheets = false;
     bool m_didCalculateResolver = false;
+
+    bool m_useCascadeOrderForShadowDOMV1 = false;
+
     OwnPtrWillBeMember<StyleResolver> m_resolver;
     StyleInvalidator m_styleInvalidator;