[CSS Grid Layout] Percentages of indefinite sizes should compute to "auto"

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 469 matching lines @@
 
     return availableLogicalSpaceIgnoringFractionTracks / accumulatedFractions;
 }
 
 const GridTrackSize& RenderGrid::gridTrackSize(GridTrackSizingDirection direction, size_t i) const
 {
     const Vector<GridTrackSize>& trackStyles = (direction == ForColumns) ? style()->gridDefinitionColumns() : style()->gridDefinitionRows();
     if (i >= trackStyles.size())
         return (direction == ForColumns) ? style()->gridAutoColumns() : style()->gridAutoRows();
 
-    return trackStyles[i];
+    const GridTrackSize& trackSize = trackStyles[i];
+    // If the logical width/height of the grid container is indefinite, percentage values are treated as <auto>.
+    if (trackSize.isPercentage()) {
+        Length logicalSize = direction == ForColumns ? style()->logicalWidth() : style()->logicalHeight();
+        if (logicalSize.isIntrinsicOrAuto()) {
+            DEFINE_STATIC_LOCAL(GridTrackSize, autoTrackSize, (Auto));
+            return autoTrackSize;
+        }
+    }
+
+    return trackSize;
 }
 
 size_t RenderGrid::explicitGridColumnCount() const
 {
     return style()->gridDefinitionColumns().size();
 }
 
 size_t RenderGrid::explicitGridRowCount() const
 {
     return style()->gridDefinitionRows().size();
@@ skipping 641 matching lines @@
     if (isOutOfFlowPositioned())
         return "RenderGrid (positioned)";
     if (isAnonymous())
         return "RenderGrid (generated)";
     if (isRelPositioned())
         return "RenderGrid (relative positioned)";
     return "RenderGrid";
 }
 
 } // namespace WebCore