[CSS Grid Layout] Handle percentages of indefinite sizes in minmax()

Source/core/rendering/style/GridLength.h

Index: Source/core/rendering/style/GridLength.h
diff --git a/Source/core/rendering/style/GridLength.h b/Source/core/rendering/style/GridLength.h
index 0e4819321d578dea4b4b4887c45da834b05e4bc3..6fd8a3aef31a39f4b95bbc02a1c648992fb9f0f4 100644
--- a/Source/core/rendering/style/GridLength.h
+++ b/Source/core/rendering/style/GridLength.h
@@ -60,6 +60,8 @@ public:
 
     double flex() const { ASSERT(isFlex()); return m_flex; }
 
+    bool isPercentage() const { return m_type == LengthType && m_length.isPercent(); }
+
     bool operator==(const GridLength& o) const
     {
         return m_length == o.m_length && m_flex == o.m_flex && m_type == o.m_type;