Introduce Node::needsDistributionRecalc and use it in ElementShadow to fix the wrong assertions.

Source/core/dom/Node.h

Index: Source/core/dom/Node.h
diff --git a/Source/core/dom/Node.h b/Source/core/dom/Node.h
index 97ae69e49cc114d5da27b42e2aa4e2d8852a6e32..f2fc1408099299ffd8c30ae2188da55b85c8be76 100644
--- a/Source/core/dom/Node.h
+++ b/Source/core/dom/Node.h
@@ -371,6 +371,10 @@ public:
     void setNeedsStyleRecalc(StyleChangeType, const StyleChangeReasonForTracing&);
     void clearNeedsStyleRecalc();
 
+#if ENABLE(ASSERT)
+    bool needsDistributionRecalc() const;
+#endif
+
     bool childNeedsDistributionRecalc() const { return getFlag(ChildNeedsDistributionRecalcFlag); }
     void setChildNeedsDistributionRecalc()  { setFlag(ChildNeedsDistributionRecalcFlag); }
     void clearChildNeedsDistributionRecalc()  { clearFlag(ChildNeedsDistributionRecalcFlag); }