[CSS Grid Layout] Speed up content sized track layout

Source/core/rendering/RenderGrid.cpp

 /*
  * Copyright (C) 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 491 matching lines @@
     return style()->gridDefinitionRows().size();
 }
 
 size_t RenderGrid::explicitGridSizeForSide(GridPositionSide side) const
 {
     return (side == ColumnStartSide || side == ColumnEndSide) ? explicitGridColumnCount() : explicitGridRowCount();
 }
 
 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();
 }
 
 LayoutUnit RenderGrid::minContentForChild(RenderBox* child, TrackSizingDirection direction, Vector<GridTrack>& columnTracks)
 {
     bool hasOrthogonalWritingMode = child->isHorizontalWritingMode() != isHorizontalWritingMode();
     // FIXME: Properly support orthogonal writing mode.
     if (hasOrthogonalWritingMode)
         return 0;
 
@@ skipping 602 matching lines @@
     if (isOutOfFlowPositioned())
         return "RenderGrid (positioned)";
     if (isAnonymous())
         return "RenderGrid (generated)";
     if (isRelPositioned())
         return "RenderGrid (relative positioned)";
     return "RenderGrid";
 }
 
 } // namespace WebCore