[css-grid] Move stretch of "auto" tracks into the track sizing algorithm

CSS WG has agreed to modify the track sizing algorithm to include
a new step: https://drafts.csswg.org/css-grid/#algo-stretch
We used to do the stretch of the "auto" tracks at the end of
the track sizing algorithm, however this change integrates it
into the algorithm itself as the last step.
See: https://github.com/w3c/csswg-drafts/issues/1150

The patch moves the method
LayoutGrid::ApplyStretchAlignmentToTracksIfNeeded() to
GridTrackSizingAlgorithm::StretchAutoTracksIfNeeded().
And then modifies the grid track sizing algorithm to execute
the new step.

This also modifies the test to check the new expected behavior.

BUG=763386
TEST=external/wpt/css/css-grid-1/grid-items/grid-minimum-size-grid-items-021.html

Change-Id: Ieb31e822989ae4655d0e632885215e4a032dd445
Reviewed-on: https://chromium-review.googlesource.com/657578
Commit-Queue: Manuel Rego Casasnovas <rego@igalia.com>
Reviewed-by: Sergio Villar <svillar@igalia.com>
Reviewed-by: Javier Fernandez <jfernandez@igalia.com>
Cr-Commit-Position: refs/heads/master@{#501249}

third_party/WebKit/LayoutTests/external/wpt/css/css-grid-1/grid-items/grid-minimum-size-grid-items-021.html

@@ -68,14 +68,14 @@
   function runTests() {
     checkGridSizeTracksAndImageSize("grid-1", "img-1", "200px", "200px", "200px", "200px", "200px", "200px");
     checkGridSizeTracksAndImageSize("grid-2", "img-2", "10px", "10px", "200px", "200px", "200px", "200px");
-    checkGridSizeTracksAndImageSize("grid-3", "img-3", "200px", "50px", "200px", "50px", "200px", "200px");
-    checkGridSizeTracksAndImageSize("grid-4", "img-4", "200px", "10px", "200px", "50px", "200px", "200px");
+    checkGridSizeTracksAndImageSize("grid-3", "img-3", "200px", "200px", "200px", "200px", "200px", "200px");
+    checkGridSizeTracksAndImageSize("grid-4", "img-4", "200px", "10px", "200px", "200px", "200px", "200px");
     checkGridSizeTracksAndImageSize("grid-5", "img-5", "200px", "50px", "50px", "50px", "50px", "50px");
     checkGridSizeTracksAndImageSize("grid-6", "img-6", "200px", "10px", "50px", "50px", "50px", "50px");
     checkGridSizeTracksAndImageSize("grid-7", "img-7", "200px", "225px", "200px", "200px 25px", "200px", "200px");
     checkGridSizeTracksAndImageSize("grid-8", "img-8", "10px", "10px", "200px", "200px 25px", "200px", "200px");
-    checkGridSizeTracksAndImageSize("grid-9", "img-9", "200px", "125px", "200px", "100px 25px", "200px", "200px");
-    checkGridSizeTracksAndImageSize("grid-10", "img-10", "200px", "10px", "200px", "100px 25px", "200px", "200px");
+    checkGridSizeTracksAndImageSize("grid-9", "img-9", "200px", "225px", "200px", "200px 25px", "200px", "200px");
+    checkGridSizeTracksAndImageSize("grid-10", "img-10", "200px", "10px", "200px", "200px 25px", "200px", "200px");
     checkGridSizeTracksAndImageSize("grid-11", "img-11", "200px", "125px", "100px", "100px 25px", "100px", "100px");
     checkGridSizeTracksAndImageSize("grid-12", "img-12", "200px", "10px", "100px", "100px 25px", "100px", "100px");
     checkGridSizeTracksAndImageSize("grid-13", "img-13", "200px", "200px", "200px", "200px", "200px", "200px");

third_party/WebKit/Source/core/layout/GridTrackSizingAlgorithm.cpp

@@ -726,6 +726,7 @@ LayoutUnit GridTrackSizingAlgorithm::InitialGrowthLimit(
 void GridTrackSizingAlgorithm::InitializeTrackSizes() {
   DCHECK(content_sized_tracks_index_.IsEmpty());
   DCHECK(flexible_sized_tracks_index_.IsEmpty());
+  DCHECK(auto_sized_tracks_index_.IsEmpty());
   Vector<GridTrack>& track_list = Tracks(direction_);
   bool has_definite_free_space = !!AvailableSpace();
   size_t num_tracks = track_list.size();
@@ -748,6 +749,8 @@ void GridTrackSizingAlgorithm::InitializeTrackSizes() {
       content_sized_tracks_index_.push_back(i);
     if (track_size.MaxTrackBreadth().IsFlex())
       flexible_sized_tracks_index_.push_back(i);
+    if (track_size.HasAutoMaxTrackBreadth())
+      auto_sized_tracks_index_.push_back(i);
   }
 }
 
@@ -1300,6 +1303,9 @@ void GridTrackSizingAlgorithm::ComputeFlexSizedTracksGrowth(
 
 void GridTrackSizingAlgorithm::StretchFlexibleTracks(
     Optional<LayoutUnit> free_space) {
+  if (flexible_sized_tracks_index_.IsEmpty())
+    return;
+
   double flex_fraction = strategy_->FindUsedFlexFraction(
       flexible_sized_tracks_index_, direction_, free_space);
 
@@ -1329,6 +1335,34 @@ void GridTrackSizingAlgorithm::StretchFlexibleTracks(
   max_content_size_ += total_growth;
 }
 
+void GridTrackSizingAlgorithm::StretchAutoTracks() {
+  if (auto_sized_tracks_index_.IsEmpty())
+    return;
+
+  Optional<LayoutUnit> free_space = FreeSpace(direction_);
+  if (!free_space || free_space.value() <= 0 ||
+      (direction_ == kForColumns &&
+       layout_grid_->StyleRef().ResolvedJustifyContentDistribution(
+           layout_grid_->ContentAlignmentNormalBehavior()) !=
+           kContentDistributionStretch) ||
+      (direction_ == kForRows &&
+       layout_grid_->StyleRef().ResolvedAlignContentDistribution(
+           layout_grid_->ContentAlignmentNormalBehavior()) !=
+           kContentDistributionStretch))
+    return;
+
+  unsigned number_of_auto_sized_tracks = auto_sized_tracks_index_.size();
+  LayoutUnit size_to_increase =
+      free_space.value() / number_of_auto_sized_tracks;
+  Vector<GridTrack>& all_tracks = Tracks(direction_);
+  for (const auto& track_index : auto_sized_tracks_index_) {
+    auto& track = all_tracks[track_index];
+    LayoutUnit base_size = track.BaseSize() + size_to_increase;
+    track.SetBaseSize(base_size);
+  }
+  SetFreeSpace(direction_, LayoutUnit());
+}
+
 void GridTrackSizingAlgorithm::AdvanceNextState() {
   switch (sizing_state_) {
     case kColumnSizingFirstIteration:
@@ -1379,6 +1413,7 @@ void GridTrackSizingAlgorithm::Setup(GridTrackSizingDirection direction,
 
   content_sized_tracks_index_.Shrink(0);
   flexible_sized_tracks_index_.Shrink(0);
+  auto_sized_tracks_index_.Shrink(0);
 
   SetFreeSpace(direction, free_space);
   Tracks(direction).resize(num_tracks);
@@ -1417,11 +1452,11 @@ void GridTrackSizingAlgorithm::Run() {
                                                     ? free_space_columns_
                                                     : free_space_rows_);
 
-  if (flexible_sized_tracks_index_.IsEmpty())
-    return;
-
   // Step 4.
   StretchFlexibleTracks(initial_free_space);
+
+  // Step 5.
+  StretchAutoTracks();
 }
 
 void GridTrackSizingAlgorithm::Reset() {
@@ -1430,6 +1465,7 @@ void GridTrackSizingAlgorithm::Reset() {
   rows_.Shrink(0);
   content_sized_tracks_index_.Shrink(0);
   flexible_sized_tracks_index_.Shrink(0);
+  auto_sized_tracks_index_.Shrink(0);
   SetAvailableSpace(kForRows, WTF::nullopt);
   SetAvailableSpace(kForColumns, WTF::nullopt);
 }

third_party/WebKit/Source/core/layout/GridTrackSizingAlgorithm.h

@@ -166,6 +166,7 @@ class GridTrackSizingAlgorithm final {
   void InitializeTrackSizes();
   void ResolveIntrinsicTrackSizes();
   void StretchFlexibleTracks(Optional<LayoutUnit> free_space);
+  void StretchAutoTracks();
 
   // State machine.
   void AdvanceNextState();
@@ -185,6 +186,7 @@ class GridTrackSizingAlgorithm final {
   Vector<GridTrack> rows_;
   Vector<size_t> content_sized_tracks_index_;
   Vector<size_t> flexible_sized_tracks_index_;
+  Vector<size_t> auto_sized_tracks_index_;
 
   GridTrackSizingDirection direction_;
 

third_party/WebKit/Source/core/layout/LayoutGrid.cpp

@@ -404,9 +404,6 @@ void LayoutGrid::UpdateBlockLayout(bool relayout_children) {
       SetLogicalHeight(
           std::max(LogicalHeight(), MinimumLogicalHeightForEmptyLine()));
 
-    ApplyStretchAlignmentToTracksIfNeeded(kForColumns);
-    ApplyStretchAlignmentToTracksIfNeeded(kForRows);
-
     LayoutGridItems();
     track_sizing_algorithm_.Reset();
 
@@ -1172,44 +1169,6 @@ const StyleContentAlignmentData& LayoutGrid::ContentAlignmentNormalBehavior() {
   return kNormalBehavior;
 }
 
-void LayoutGrid::ApplyStretchAlignmentToTracksIfNeeded(
-    GridTrackSizingDirection direction) {
-  Optional<LayoutUnit> free_space =
-      track_sizing_algorithm_.FreeSpace(direction);
-  if (!free_space || free_space.value() <= 0 ||
-      (direction == kForColumns &&
-       StyleRef().ResolvedJustifyContentDistribution(
-           ContentAlignmentNormalBehavior()) != kContentDistributionStretch) ||
-      (direction == kForRows &&
-       StyleRef().ResolvedAlignContentDistribution(
-           ContentAlignmentNormalBehavior()) != kContentDistributionStretch))
-    return;
-
-  // Spec defines auto-sized tracks as the ones with an 'auto' max-sizing
-  // function.
-  Vector<GridTrack>& all_tracks = track_sizing_algorithm_.Tracks(direction);
-  Vector<unsigned> auto_sized_tracks_index;
-  for (unsigned i = 0; i < all_tracks.size(); ++i) {
-    const GridTrackSize& track_size =
-        track_sizing_algorithm_.GetGridTrackSize(direction, i);
-    if (track_size.HasAutoMaxTrackBreadth())
-      auto_sized_tracks_index.push_back(i);
-  }
-
-  unsigned number_of_auto_sized_tracks = auto_sized_tracks_index.size();
-  if (number_of_auto_sized_tracks < 1)
-    return;
-
-  LayoutUnit size_to_increase =
-      free_space.value() / number_of_auto_sized_tracks;
-  for (const auto& track_index : auto_sized_tracks_index) {
-    GridTrack* track = all_tracks.data() + track_index;
-    LayoutUnit base_size = track->BaseSize() + size_to_increase;
-    track->SetBaseSize(base_size);
-  }
-  track_sizing_algorithm_.SetFreeSpace(direction, LayoutUnit());
-}
-
 void LayoutGrid::LayoutGridItems() {
   PopulateGridPositionsForDirection(kForColumns);
   PopulateGridPositionsForDirection(kForRows);

third_party/WebKit/Source/core/layout/LayoutGrid.h

@@ -106,6 +106,8 @@ class LayoutGrid final : public LayoutBlock {
   LayoutUnit GridGap(GridTrackSizingDirection) const;
   LayoutUnit GridItemOffset(GridTrackSizingDirection) const;
 
+  static const StyleContentAlignmentData& ContentAlignmentNormalBehavior();
+
  protected:
   ItemPosition SelfAlignmentNormalBehavior(
       const LayoutBox* child = nullptr) const override {
@@ -211,8 +213,6 @@ class LayoutGrid final : public LayoutBlock {
       const LayoutBox&,
       GridTrackSizingDirection) const;
 
-  void ApplyStretchAlignmentToTracksIfNeeded(GridTrackSizingDirection);
-
   void PaintChildren(const PaintInfo&, const LayoutPoint&) const override;
 
   LayoutUnit AvailableAlignmentSpaceForChildBeforeStretching(
@@ -297,7 +297,6 @@ class LayoutGrid final : public LayoutBlock {
                                                       LineDirectionMode);
   static LayoutUnit SynthesizedBaselineFromBorderBox(const LayoutBox&,
                                                      LineDirectionMode);
-  static const StyleContentAlignmentData& ContentAlignmentNormalBehavior();
 
   typedef HashMap<unsigned,
                   std::unique_ptr<BaselineContext>,