[CSS Grid Layout] Flex factor sum must be 1 at least.

Source/core/layout/LayoutGrid.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 557 matching lines @@
                 break;
 
             fractionValueBasedOnGridItemsRatio = track.m_normalizedFlexValue;
         }
 
         accumulatedFractions += track.m_flex;
         // This item was processed so we re-add its used breadth to the available space to accurately count the remaining space.
         availableLogicalSpaceIgnoringFractionTracks += track.m_track->baseSize();
     }
 
+    // Let flex factor sum be the sum of the flex factors of the flexible tracks. If this value
+    // is less than 1, set it to 1 instead.
+    if (accumulatedFractions < 1)
+        return availableLogicalSpaceIgnoringFractionTracks;
+
     return availableLogicalSpaceIgnoringFractionTracks / accumulatedFractions;
 }
 
 bool LayoutGrid::hasDefiniteLogicalSize(GridTrackSizingDirection direction) const
 {
     return (direction == ForRows) ? hasDefiniteLogicalHeight() : hasDefiniteLogicalWidth();
 }
 
 GridTrackSize LayoutGrid::gridTrackSize(GridTrackSizingDirection direction, size_t i) const
 {
@@ skipping 1331 matching lines @@
 
     return LayoutPoint(rowAxisOffset, columnAxisOffsetForChild(child));
 }
 
 void LayoutGrid::paintChildren(const PaintInfo& paintInfo, const LayoutPoint& paintOffset)
 {
     GridPainter(*this).paintChildren(paintInfo, paintOffset);
 }
 
 } // namespace blink