[CSS Grid Layout] Speed up content sized track layout

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 9d0d58990de04c5fe7aeb8b1dee48edbb24739b6..36530fb98d2bdc580428766e73168c2e9758cb69 100644
--- a/Source/core/rendering/RenderGrid.cpp
+++ b/Source/core/rendering/RenderGrid.cpp
@@ -509,18 +509,14 @@ size_t RenderGrid::explicitGridSizeForSide(GridPositionSide side) const
 
 LayoutUnit RenderGrid::logicalContentHeightForChild(RenderBox* child, Vector<GridTrack>& columnTracks)
 {
-    // FIXME: We shouldn't force a layout every time this function is called but
-    // 1) Return computeLogicalHeight's value if it's available. Unfortunately computeLogicalHeight
-    // doesn't return if the logical height is available so would need to be changed.
-    // 2) Relayout if the column track's used breadth changed OR the logical height is unavailable.
-    if (!child->needsLayout())
+    if (child->style()->logicalHeight().isPercent())

[ojan, 2013/08/13 17:22:21]

What if it's position:absolute; top:0; bottom: 0? Does that not also hit this?
Do we get that case wrong today?

[Julien - ping for review, 2013/08/13 18:45:43]

Absolutely positioned grid items don't participate in the layout per the
specification (http://dev.w3.org/csswg/css-grid/#abspos-items)
I am pretty sure we don't handle that properly due to lack of testing around
absolutely positioned grid items.

         child->setNeedsLayout(MarkOnlyThis);
 
     child->setOverrideContainingBlockContentLogicalWidth(gridAreaBreadthForChild(child, ForColumns, columnTracks));
     // If |child| has a percentage logical height, we shouldn't let it override its intrinsic height, which is
     // what we are interested in here. Thus we need to set the override logical height to -1 (no possible resolution).
     child->setOverrideContainingBlockContentLogicalHeight(-1);
-    child->layout();
+    child->layoutIfNeeded();
     return child->logicalHeight();
 }