[CSS Grid Layout] CSSParser should reject <track-list> without a <track-size>

Source/core/css/resolver/StyleResolver.cpp

Index: Source/core/css/resolver/StyleResolver.cpp
diff --git a/Source/core/css/resolver/StyleResolver.cpp b/Source/core/css/resolver/StyleResolver.cpp
index ab4edfdea60a7ac4b8590f93b8a5a074cbaf69fa..25412b43adac2e31670dab0935bbece33c57a127 100644
--- a/Source/core/css/resolver/StyleResolver.cpp
+++ b/Source/core/css/resolver/StyleResolver.cpp
@@ -2303,9 +2303,9 @@ static bool createGridTrackList(CSSValue* value, Vector<GridTrackSize>& trackSiz
         trackSizes.append(trackSize);
     }
 
-    if (trackSizes.isEmpty())
-        return false;
-
+    // The parser should have rejected any <track-list> without any <track-size> as
+    // this is not conformant to the syntax.
+    ASSERT(!trackSizes.isEmpty());
     return true;
 }