LibWeb: Use a special value to represent an infinite growth limit in GFC

This is preparation for introducing fixed-point CSSPixels in upcoming
commits.

Infinity is a valid state for the growth limit value of a grid track.
It was possible to use INFINITY when CSSPixels were represented using
floating point, but it won't work after the transition to fixed point,
which is represented using integers. This change addresses this by
using -1 as a special value to represent the infinite state of the
growth limit.

Userland/Libraries/LibWeb/Layout/GridFormattingContext.cpp

@@ -10,6 +10,8 @@
 
 namespace Web::Layout {
 
+static int const infinity = -1;
+
 GridFormattingContext::GridTrack GridFormattingContext::GridTrack::create_from_definition(CSS::ExplicitGridTrack const& definition)
 {
     // NOTE: repeat() is expected to be expanded beforehand.
@@ -718,16 +720,16 @@ void GridFormattingContext::initialize_track_sizes(AvailableSpace const& availab
         if (track.max_track_sizing_function.is_fixed(available_size)) {
             track.growth_limit = track.max_track_sizing_function.css_size().to_px(grid_container(), available_size.to_px());
         } else if (track.max_track_sizing_function.is_flexible_length()) {
-            track.growth_limit = INFINITY;
+            track.growth_limit = infinity;
         } else if (track.max_track_sizing_function.is_intrinsic(available_size)) {
-            track.growth_limit = INFINITY;
+            track.growth_limit = infinity;
         } else {
             VERIFY_NOT_REACHED();
         }
 
         // In all cases, if the growth limit is less than the base size, increase the growth limit to match
         // the base size.
-        if (track.growth_limit < track.base_size)
+        if (track.growth_limit != infinity && track.growth_limit < track.base_size)
             track.growth_limit = track.base_size;
     }
 }
@@ -766,7 +768,7 @@ void GridFormattingContext::resolve_intrinsic_track_sizes(AvailableSpace const&
     // 5. If any track still has an infinite growth limit (because, for example, it had no items placed in
     // it or it is a flexible track), set its growth limit to its base size.
     for (auto& track : tracks_and_gaps) {
-        if (!isfinite(track.growth_limit.to_double())) {
+        if (track.growth_limit == infinity) {
             track.growth_limit = track.base_size;
         }
     }
@@ -811,7 +813,7 @@ void GridFormattingContext::distribute_extra_space_across_spanned_tracks_base_si
             if (track.base_size_frozen)
                 continue;
 
-            if (increase_per_track >= track.growth_limit) {
+            if (track.growth_limit != infinity && increase_per_track >= track.growth_limit) {
                 track.base_size_frozen = true;
                 track.item_incurred_increase = track.growth_limit;
                 extra_space -= track.growth_limit;
@@ -871,7 +873,7 @@ void GridFormattingContext::distribute_extra_space_across_spanned_tracks_growth_
     // 1. Find the space to distribute:
     CSSPixels spanned_tracks_sizes_sum = 0;
     for (auto& track : spanned_tracks) {
-        if (isfinite(track.growth_limit.to_double())) {
+        if (track.growth_limit != infinity) {
             spanned_tracks_sizes_sum += track.growth_limit;
         } else {
             spanned_tracks_sizes_sum += track.base_size;
@@ -900,8 +902,8 @@ void GridFormattingContext::distribute_extra_space_across_spanned_tracks_growth_
 
             // For growth limits, the limit is infinity if it is marked as infinitely growable, and equal to the
             // growth limit otherwise.
-            auto limit = track.infinitely_growable ? INFINITY : track.growth_limit;
-            if (increase_per_track >= limit) {
+            auto limit = track.infinitely_growable ? infinity : track.growth_limit;
+            if (limit != infinity && increase_per_track >= limit) {
                 track.growth_limit_frozen = true;
                 track.item_incurred_increase = limit;
                 extra_space -= limit;
@@ -988,7 +990,7 @@ void GridFormattingContext::increase_sizes_to_accommodate_spanning_items_crossin
         // 4. If at this point any track’s growth limit is now less than its base size, increase its growth limit to
         //    match its base size.
         for (auto& track : tracks) {
-            if (track.growth_limit < track.base_size)
+            if (track.growth_limit != infinity && track.growth_limit < track.base_size)
                 track.growth_limit = track.base_size;
         }
 
@@ -997,7 +999,7 @@ void GridFormattingContext::increase_sizes_to_accommodate_spanning_items_crossin
             return track.max_track_sizing_function.is_intrinsic(available_size);
         });
         for (auto& track : spanned_tracks) {
-            if (!isfinite(track.growth_limit.to_double())) {
+            if (track.growth_limit == infinity) {
                 // If the affected size is an infinite growth limit, set it to the track’s base size plus the planned increase.
                 track.growth_limit = track.base_size + track.planned_increase;
                 // Mark any tracks whose growth limit changed from infinite to finite in this step as infinitely growable
@@ -1017,7 +1019,7 @@ void GridFormattingContext::increase_sizes_to_accommodate_spanning_items_crossin
             return track.max_track_sizing_function.is_max_content() || track.max_track_sizing_function.is_auto(available_size);
         });
         for (auto& track : spanned_tracks) {
-            if (!isfinite(track.growth_limit.to_double())) {
+            if (track.growth_limit == infinity) {
                 // If the affected size is an infinite growth limit, set it to the track’s base size plus the planned increase.
                 track.growth_limit = track.base_size + track.planned_increase;
             } else {
@@ -1058,7 +1060,7 @@ void GridFormattingContext::increase_sizes_to_accommodate_spanning_items_crossin
         // 4. If at this point any track’s growth limit is now less than its base size, increase its growth limit to
         //    match its base size.
         for (auto& track : tracks) {
-            if (track.growth_limit < track.base_size)
+            if (track.growth_limit != infinity && track.growth_limit < track.base_size)
                 track.growth_limit = track.base_size;
         }
     }
@@ -1093,7 +1095,7 @@ void GridFormattingContext::maximize_tracks(AvailableSpace const& available_spac
         for (auto& track : tracks) {
             if (track.base_size_frozen)
                 continue;
-            VERIFY(isfinite(track.growth_limit.to_double()));
+            VERIFY(track.growth_limit != infinity);
             track.base_size = min(track.growth_limit, track.base_size + free_space_to_distribute_per_track);
         }
         if (get_free_space_px() == free_space_px)