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

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 68f2e3e6d425ab54323c3128dda9775cc08c2d17..9fe86f921f9566bfb7e9c5cd7b3757c302739b49 100644
--- a/Source/core/rendering/RenderGrid.cpp
+++ b/Source/core/rendering/RenderGrid.cpp
@@ -488,7 +488,17 @@ const GridTrackSize& RenderGrid::gridTrackSize(GridTrackSizingDirection directio
     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.isSpecified()) {

[Julien - ping for review, 2013/11/07 18:18:26]

This is not totally right but a good beginning.

isSpecified will return true for <percentage>, when "indefinite size" has a
different meaning (we should ignore a <percentage> that is not resolved against
a definite size). I don't think we have an API that would return that.

[svillar, 2013/11/07 18:44:29]

I don't really get what you mean with "when indefinite size has a different
meaning". I understand that you think isSpecified() is not equal to "definite
size" right? I agree, the thing is that I am not sure there is such a check in
the current code.

+            DEFINE_STATIC_LOCAL(GridTrackSize, autoTrackSize, (Auto));
+            return autoTrackSize;
+        }
+    }
+
+    return trackSize;
 }
 
 size_t RenderGrid::explicitGridColumnCount() const