[CSS Grid Layout] Add GridSpan::iterator

Source/core/rendering/style/GridResolvedPosition.h

Index: Source/core/rendering/style/GridResolvedPosition.h
diff --git a/Source/core/rendering/style/GridResolvedPosition.h b/Source/core/rendering/style/GridResolvedPosition.h
index e9a32a2164fa6471e125c95cc576edd9b53c629b..9de016b8d2e97f58e9457c3eea7a5f83d2f65ee1 100644
--- a/Source/core/rendering/style/GridResolvedPosition.h
+++ b/Source/core/rendering/style/GridResolvedPosition.h
@@ -74,6 +74,11 @@ public:
         return m_integerPosition == other.m_integerPosition;
     }
 
+    bool operator!=(const GridResolvedPosition& other) const
+    {
+        return m_integerPosition != other.m_integerPosition;
+    }
+
     bool operator<(const GridResolvedPosition& other) const
     {
         return m_integerPosition < other.m_integerPosition;
@@ -99,6 +104,11 @@ public:
         return m_integerPosition;
     }
 
+    GridResolvedPosition next() const
+    {
+        return GridResolvedPosition(m_integerPosition + 1);
+    }
+
     static size_t explicitGridColumnCount(const RenderStyle&);
     static size_t explicitGridRowCount(const RenderStyle&);