[CSS Grid Layout] Fix issues adding new items to grid

Source/core/rendering/RenderGrid.cpp

Index: Source/core/rendering/RenderGrid.cpp
diff --git a/Source/core/rendering/RenderGrid.cpp b/Source/core/rendering/RenderGrid.cpp
index 351881084b582f24de06651ade28f7fd5595239d..96f1dde74f08210cebf0afbf4bb3bf694d5c36eb 100644
--- a/Source/core/rendering/RenderGrid.cpp
+++ b/Source/core/rendering/RenderGrid.cpp
@@ -191,20 +191,28 @@ void RenderGrid::addChild(RenderObject* newChild, RenderObject* beforeChild)
         return;
     }
 
+    if (style()->gridAutoFlow() != AutoFlowNone) {
+        // The grid needs to be recomputed as it might contain auto-placed items that will change their position.
+        dirtyGrid();
+        return;
+    }
+
     RenderBox* newChildBox = toRenderBox(newChild);
     OwnPtr<GridSpan> rowPositions = resolveGridPositionsFromStyle(newChildBox, ForRows);
     OwnPtr<GridSpan> columnPositions = resolveGridPositionsFromStyle(newChildBox, ForColumns);
     if (!rowPositions || !columnPositions) {
         // The new child requires the auto-placement algorithm to run so we need to recompute the grid fully.
         dirtyGrid();
-    } else {
-        if (gridRowCount() <= rowPositions->finalPositionIndex || gridColumnCount() <= columnPositions->finalPositionIndex) {
-            // FIXME: We could just insert the new child provided we had a primitive to arbitrarily grow the grid.
-            dirtyGrid();
-        } else {
-            insertItemIntoGrid(newChildBox, GridCoordinate(*rowPositions, *columnPositions));
-        }
+        return;

[Julien - ping for review, 2014/03/21 04:10:35]

Not sure what the return brings us here as it really was an else below :-)

     }
+
+    // Grow grid if required.
+    for (size_t i = gridRowCount(); i <= rowPositions->finalPositionIndex; i++)
+        growGrid(ForRows);
+    for (size_t i = gridColumnCount(); i <= columnPositions->finalPositionIndex; i++)
+        growGrid(ForColumns);

[Julien - ping for review, 2014/03/21 04:10:35]

I have been thinking that we need a way to grow the grid more than a single item
at a time. This is for efficiency as well as to support auto-placement with
spanning items.

+
+    insertItemIntoGrid(newChildBox, GridCoordinate(*rowPositions, *columnPositions));
 }
 
 void RenderGrid::removeChild(RenderObject* child)