[CSS Grid Layout] Introduce an explicit type for resolved grid positions

Source/core/rendering/style/GridResolvedPosition.h

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef GridResolvedPosition_h
+#define GridResolvedPosition_h
+
+#include "core/rendering/style/GridPosition.h"
+
+namespace WebCore {
+
+enum GridPositionSide {
+    ColumnStartSide,
+    ColumnEndSide,
+    RowStartSide,
+    RowEndSide
+};
+
+class GridResolvedPosition {
+public:
+    static size_t adjustGridPositionForAfterEndSide(size_t resolvedPosition)
+    {
+        return resolvedPosition ? resolvedPosition - 1 : 0;
+    }
+
+    static size_t adjustGridPositionForSide(size_t resolvedPosition, GridPositionSide side)
+    {
+        // An item finishing on the N-th line belongs to the N-1-th cell.
+        if (side == ColumnEndSide || side == RowEndSide)
+            return adjustGridPositionForAfterEndSide(resolvedPosition);
+
+        return resolvedPosition;
+    }
+
+    GridResolvedPosition()
+        : m_integerPosition(0)
+    {
+    }

[Julien - ping for review, 2014/03/06 22:38:02]

IMHO we should just not have this constructor and always be explicit.

+
+    GridResolvedPosition(size_t position)
+        : m_integerPosition(position)
+    {
+    }
+
+    GridResolvedPosition(const GridPosition& position, GridPositionSide side)
+    {
+        size_t integerPosition;
+
+        ASSERT(position.integerPosition());
+        integerPosition = position.integerPosition() - 1;
+
+        m_integerPosition = adjustGridPositionForSide(integerPosition, side);
+    }
+
+    size_t integerPosition() const

[Julien - ping for review, 2014/03/06 22:38:02]

Do we need the explicit "integer" in the getter/setter? I would expect a
resolved position to be an index so it can't be anything but an integer.

+    {
+        return m_integerPosition;
+    }
+
+    void setIntegerPosition(size_t position)
+    {
+        m_integerPosition = position;
+    }
+

[Julien - ping for review, 2014/03/06 22:38:02]

The current API makes the code very verbose as we have to explicitly doing int
conversions.

It would be nice to implement the following:
- some comparison operators on GridResolvedPosition (<, <=, >, ...) between
GridResolvedPosition (and maybe also int?)
- void setPosition(const GridResolvedPosition&)
- operator int() (<- I am not really sure about this one as it would allow to
easily mix int / GridResolvedPosition and probably contained in the first
suggestion)

+private:
+    size_t m_integerPosition;
+};
+
+} // namespace WebCore
+
+#endif // GridResolvedPosition_h