Fix handling of 'inherit' and 'initial' for grid lines

Source/core/rendering/style/StyleGridItemData.cpp

Index: Source/core/rendering/style/StyleGridItemData.cpp
diff --git a/Source/core/rendering/style/StyleGridItemData.cpp b/Source/core/rendering/style/StyleGridItemData.cpp
index 011baa89ad3444dfca37830f03e38b2d3e9a77d9..ea938043375c93126c16abc41091ab87c692c64f 100644
--- a/Source/core/rendering/style/StyleGridItemData.cpp
+++ b/Source/core/rendering/style/StyleGridItemData.cpp
@@ -35,10 +35,10 @@
 namespace WebCore {
 
 StyleGridItemData::StyleGridItemData()
-    : m_gridStart(RenderStyle::initialGridPosition())
-    , m_gridEnd(RenderStyle::initialGridPosition())
-    , m_gridBefore(RenderStyle::initialGridPosition())
-    , m_gridAfter(RenderStyle::initialGridPosition())
+    : m_gridStart(RenderStyle::initialGridStart())
+    , m_gridEnd(RenderStyle::initialGridEnd())
+    , m_gridBefore(RenderStyle::initialGridBefore())
+    , m_gridAfter(RenderStyle::initialGridAfter())
 {
 }