[css-grid] Implement grid gutters

Source/core/style/ComputedStyle.h

Index: Source/core/style/ComputedStyle.h
diff --git a/Source/core/style/ComputedStyle.h b/Source/core/style/ComputedStyle.h
index 117fb60cf668787863416156eacd38432b71f153..8aa317876d9d911455905b62bba41195f4af12ee 100644
--- a/Source/core/style/ComputedStyle.h
+++ b/Source/core/style/ComputedStyle.h
@@ -791,6 +791,9 @@ public:
     bool isGridAutoFlowAlgorithmDense() const { return (rareNonInheritedData->m_grid->m_gridAutoFlow & InternalAutoFlowAlgorithmDense) == InternalAutoFlowAlgorithmDense; }
     const GridTrackSize& gridAutoColumns() const { return rareNonInheritedData->m_grid->m_gridAutoColumns; }
     const GridTrackSize& gridAutoRows() const { return rareNonInheritedData->m_grid->m_gridAutoRows; }
+    const Length& gridColumnGap() const { return rareNonInheritedData->m_grid->m_gridColumnGap; }
+    const Length& gridRowGap() const { return rareNonInheritedData->m_grid->m_gridRowGap; }
+
 
     const GridPosition& gridColumnStart() const { return rareNonInheritedData->m_gridItem->m_gridColumnStart; }
     const GridPosition& gridColumnEnd() const { return rareNonInheritedData->m_gridItem->m_gridColumnEnd; }
@@ -1318,6 +1321,8 @@ public:
     void setGridColumnEnd(const GridPosition& columnEndPosition) { SET_VAR(rareNonInheritedData.access()->m_gridItem, m_gridColumnEnd, columnEndPosition); }
     void setGridRowStart(const GridPosition& rowStartPosition) { SET_VAR(rareNonInheritedData.access()->m_gridItem, m_gridRowStart, rowStartPosition); }
     void setGridRowEnd(const GridPosition& rowEndPosition) { SET_VAR(rareNonInheritedData.access()->m_gridItem, m_gridRowEnd, rowEndPosition); }
+    void setGridColumnGap(const Length& v) { SET_VAR(rareNonInheritedData.access()->m_grid, m_gridColumnGap, v); }
+    void setGridRowGap(const Length& v) { SET_VAR(rareNonInheritedData.access()->m_grid, m_gridRowGap, v); }
 
     void setUserModify(EUserModify u) { SET_VAR(rareInheritedData, userModify, u); }
     void setUserDrag(EUserDrag d) { SET_VAR(rareNonInheritedData, userDrag, d); }
@@ -1732,6 +1737,9 @@ public:
     static NamedGridAreaMap initialNamedGridArea() { return NamedGridAreaMap(); }
     static size_t initialNamedGridAreaCount() { return 0; }
 
+    static Length initialGridColumnGap() { return Length(Fixed); }
+    static Length initialGridRowGap() { return Length(Fixed); }
+
     // 'auto' is the default.
     static GridPosition initialGridColumnStart() { return GridPosition(); }
     static GridPosition initialGridColumnEnd() { return GridPosition(); }