Fix RenderBlock::percentHeightDescendants()

Source/core/rendering/RenderBlock.h

Index: Source/core/rendering/RenderBlock.h
diff --git a/Source/core/rendering/RenderBlock.h b/Source/core/rendering/RenderBlock.h
index b11db7439d555d820f87d6886d24ef90f25f5490..86ff13e4acac1fa32818e7c0fcfe892ba6762ccb 100644
--- a/Source/core/rendering/RenderBlock.h
+++ b/Source/core/rendering/RenderBlock.h
@@ -120,12 +120,18 @@ public:
 
     void addPercentHeightDescendant(RenderBox*);
     static void removePercentHeightDescendant(RenderBox*);
-    TrackedRendererListHashSet* percentHeightDescendants() const;
     static bool hasPercentHeightContainerMap();
     static bool hasPercentHeightDescendant(RenderBox*);
     static void clearPercentHeightDescendantsFrom(RenderBox*);
     static void removePercentHeightDescendantIfNeeded(RenderBox*);
 
+    TrackedRendererListHashSet* percentHeightDescendants() const;
+    bool hasPercentHeightDescendants() const
+    {
+        TrackedRendererListHashSet* descendants = percentHeightDescendants();
+        return descendants && !descendants->isEmpty();
+    }
+
     void setHasMarkupTruncation(bool b) { m_hasMarkupTruncation = b; }
     bool hasMarkupTruncation() const { return m_hasMarkupTruncation; }