[GridNG] Fix off-by-one error in placement overlap detection.

Also added relevant testing.

Bug: 1045599
Change-Id: I514c2a827eb1d040af93c27ef1edc15d22fdddc2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2459786
Commit-Queue: Jacques Newman <janewman@microsoft.com>
Reviewed-by: Ethan Jimenez <ethavar@microsoft.com>
Reviewed-by: Christian Biesinger <cbiesinger@chromium.org>
Reviewed-by: Kurt Catti-Schmidt <kschmi@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#815255}

third_party/blink/renderer/core/layout/ng/grid/ng_grid_layout_algorithm_test.cc

@@ -20,6 +20,12 @@ namespace {
   EXPECT_EQ(expected_count, iterator.RepeatCount());                        \
   EXPECT_EQ(expected_start + expected_count - 1, iterator.RangeTrackEnd()); \
   EXPECT_TRUE(iterator.IsRangeCollapsed());
+#define EXPECT_GRID_AREA(area, expected_row_start, expected_row_end, \
+                         expected_column_start, expected_column_end) \
+  EXPECT_EQ(area.rows.StartLine(), expected_row_start);              \
+  EXPECT_EQ(area.rows.EndLine(), expected_row_end);                  \
+  EXPECT_EQ(area.columns.StartLine(), expected_column_start);        \
+  EXPECT_EQ(area.columns.EndLine(), expected_column_end);
 }  // namespace
 class NGGridLayoutAlgorithmTest
     : public NGBaseLayoutAlgorithmTest,
@@ -68,6 +74,14 @@ class NGGridLayoutAlgorithmTest
     return results;
   }
 
+  Vector<GridArea> GridItemGridAreas(const NGGridLayoutAlgorithm& algorithm) {
+    Vector<GridArea> results;
+    for (const auto& item : algorithm.items_) {
+      results.push_back(item.resolved_position);
+    }
+    return results;
+  }
+
   void DetermineGridItemsSpanningIntrinsicOrFlexTracks(
       NGGridLayoutAlgorithm& algorithm,
       GridTrackSizingDirection track_direction) {
@@ -726,6 +740,81 @@ TEST_F(NGGridLayoutAlgorithmTest, NGGridLayoutAlgorithmRangesImplicitMixed) {
   EXPECT_FALSE(row_iterator.MoveToNextRange());
 }
 
+TEST_F(NGGridLayoutAlgorithmTest, NGGridLayoutAlgorithmAutoGridPositions) {
+  if (!RuntimeEnabledFeatures::LayoutNGGridEnabled())
+    return;
+
+  SetBodyInnerHTML(R"HTML(
+  <style>
+      body {
+        font: 10px/1 Ahem;
+      }
+      #grid {
+        display: grid;
+        width: 400px;
+        height: 400px;
+        grid-template-columns: 100px 100px;
+        grid-template-rows: 100px 100px;
+      }
+      .grid_item1 {
+        display: block;
+        width: 100px;
+        height: 100px;
+        grid-row: 2;
+        grid-column: 2;
+      }
+      .grid_item2 {
+        display: block;
+        width: 90px;
+        height: 90px;
+      }
+      .grid_item3 {
+        display: block;
+        width: 80px;
+        height: 80px;
+      }
+      .grid_item4 {
+        display: block;
+        width: 70px;
+        height: 70px;
+        grid-row: 1;
+        grid-column: 1;
+      }
+    </style>
+    <div id="wrapper">
+      <div id="grid">
+        <div class="grid_item1">1</div>
+        <div class="grid_item2">2</div>
+        <div class="grid_item3">3</div>
+        <div class="grid_item4">4</div>
+      </div>
+    </div>
+
+  )HTML");
+
+  NGBlockNode node(ToLayoutBox(GetLayoutObjectByElementId("grid")));
+
+  NGConstraintSpace space = ConstructBlockLayoutTestConstraintSpace(
+      WritingMode::kHorizontalTb, TextDirection::kLtr,
+      LogicalSize(LayoutUnit(500), LayoutUnit(500)), false, true);
+
+  NGFragmentGeometry fragment_geometry =
+      CalculateInitialFragmentGeometry(space, node);
+
+  NGGridLayoutAlgorithm algorithm({node, fragment_geometry, space});
+  EXPECT_EQ(GridItemCount(algorithm), 0U);
+  algorithm.Layout();
+  EXPECT_EQ(GridItemCount(algorithm), 4U);
+
+  Vector<GridArea> grid_positions = GridItemGridAreas(algorithm);
+  ASSERT_EQ(grid_positions.size(), 4U);
+
+  EXPECT_GRID_AREA(grid_positions[0], 1U, 2U, 1U, 2U);
+  EXPECT_GRID_AREA(grid_positions[1], 0U, 1U, 1U, 2U);
+  EXPECT_GRID_AREA(grid_positions[2], 1U, 2U, 0U, 1U);
+  EXPECT_GRID_AREA(grid_positions[3], 0U, 1U, 0U, 1U);
+}
+
 TEST_F(NGGridLayoutAlgorithmTest, NGGridLayoutAlgorithmGridPositions) {
   if (!RuntimeEnabledFeatures::LayoutNGGridEnabled())
     return;

third_party/blink/renderer/core/layout/ng/grid/ng_grid_placement.cc

@@ -242,7 +242,7 @@ bool NGGridPlacement::DoesItemOverlap(wtf_size_t major_start,
     // No collision if both start and end are on the same side of the item.
     wtf_size_t item_major_start = grid_item.StartLine(major_direction_);
     wtf_size_t item_major_end = grid_item.EndLine(major_direction_);
-    if (major_end < item_major_start)
+    if (major_end <= item_major_start)
       continue;
     if (major_start >= item_major_end)
       continue;
@@ -252,7 +252,7 @@ bool NGGridPlacement::DoesItemOverlap(wtf_size_t major_start,
       continue;
     wtf_size_t item_minor_start = grid_item.StartLine(minor_direction_);
     wtf_size_t item_minor_end = grid_item.EndLine(minor_direction_);
-    if (minor_end < item_minor_start)
+    if (minor_end <= item_minor_start)
       continue;
     if (minor_start >= item_minor_end)
       continue;