[CSS Grid Layout] infinity should be defined as a negative value

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 b1e831240b2e1e55e831c7cbac4648d30f29677d..837e189c51a5550da3f8eae5af4e09a4b2f776da 100644
--- a/Source/core/rendering/RenderGrid.cpp
+++ b/Source/core/rendering/RenderGrid.cpp
@@ -33,7 +33,7 @@
 
 namespace WebCore {
 
-static const int infinity = intMaxForLayoutUnit;
+static const int infinity = -1;
 
 class GridTrack {
 public:
@@ -354,8 +354,7 @@ LayoutUnit RenderGrid::computeUsedBreadthOfMaxLength(TrackSizingDirection direct
     ASSERT(!trackLength.isAuto());
     if (trackLength.isFixed() || trackLength.isPercent() || trackLength.isViewportPercentage()) {
         LayoutUnit computedBreadth = computeUsedBreadthOfSpecifiedLength(direction, trackLength);
-        // FIXME: We should ASSERT that computedBreadth cannot return infinity but it's currently
-        // possible. See https://bugs.webkit.org/show_bug.cgi?id=107053
+        ASSERT(computedBreadth != infinity);
         return computedBreadth;
     }