[LayoutNG] Overflow control hit-testing.

This was missing when hit-testing a NG fragment (rather than the
LayoutObject).

I don't know how to write a WPT for this, but this fixes at least the
following tests with LayoutNGFragmentTraversal enabled:
  fast/events/scrollbar-double-click.html
  fast/events/touch/gesture/gesture-scrollbar-touchscreen-fling.html
  fast/events/touch/gesture/gesture-scrollbar.html

Bug: 1043787
Change-Id: I8669a16fe0d8762f29ba7a7600bcf7fa161e594f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2048084
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#740619}

third_party/blink/renderer/core/layout/layout_block.cc

@@ -1176,7 +1176,7 @@ bool LayoutBlock::IsPointInOverflowControl(
 bool LayoutBlock::HitTestOverflowControl(
     HitTestResult& result,
     const HitTestLocation& hit_test_location,
-    const PhysicalOffset& adjusted_location) {
+    const PhysicalOffset& adjusted_location) const {
   if (VisibleToHitTestRequest(result.GetHitTestRequest()) &&
       IsPointInOverflowControl(result, hit_test_location.Point(),
                                adjusted_location)) {

third_party/blink/renderer/core/layout/layout_block.h

@@ -426,9 +426,10 @@ class CORE_EXPORT LayoutBlock : public LayoutBox {
     return false;
   }
 
-  bool HitTestOverflowControl(HitTestResult&,
-                              const HitTestLocation&,
-                              const PhysicalOffset& adjusted_location) override;
+  bool HitTestOverflowControl(
+      HitTestResult&,
+      const HitTestLocation&,
+      const PhysicalOffset& adjusted_location) const override;
   bool HitTestChildren(HitTestResult&,
                        const HitTestLocation&,
                        const PhysicalOffset& accumulated_offset,

third_party/blink/renderer/core/layout/layout_box.h

@@ -1515,6 +1515,12 @@ class CORE_EXPORT LayoutBox : public LayoutBoxModelObject {
       const HitTestLocation&,
       const PhysicalOffset& border_box_location) const;
 
+  virtual bool HitTestOverflowControl(HitTestResult&,
+                                      const HitTestLocation&,
+                                      const PhysicalOffset&) const {
+    return false;
+  }
+
   // Returns true if the box intersects the viewport visible to the user.
   bool IntersectsVisibleViewport() const;
 
@@ -1659,11 +1665,6 @@ class CORE_EXPORT LayoutBox : public LayoutBoxModelObject {
 
   LayoutObject* SplitAnonymousBoxesAroundChild(LayoutObject* before_child);
 
-  virtual bool HitTestOverflowControl(HitTestResult&,
-                                      const HitTestLocation&,
-                                      const PhysicalOffset&) {
-    return false;
-  }
   virtual bool HitTestChildren(HitTestResult&,
                                const HitTestLocation&,
                                const PhysicalOffset& accumulated_offset,

third_party/blink/renderer/core/paint/ng/ng_box_fragment_painter.cc

@@ -1651,11 +1651,9 @@ bool NGBoxFragmentPainter::NodeAtPoint(const HitTestContext& hit_test,
 
   bool hit_test_self = IsInSelfHitTestingPhase(hit_test.action);
 
-  // TODO(layout-dev): Add support for hit testing overflow controls once we
-  // overflow has been implemented.
-  // if (hit_test_self && HasOverflowClip() &&
-  //   HitTestOverflowControl(result, hit_test_location, physical_offset))
-  // return true;
+  if (hit_test_self && box_fragment_.HasOverflowClip() &&
+      HitTestOverflowControl(hit_test, physical_offset))
+    return true;
 
   bool skip_children = hit_test.result->GetHitTestRequest().GetStopNode() ==
                        PhysicalFragment().GetLayoutObject();
@@ -2245,4 +2243,13 @@ bool NGBoxFragmentPainter::HitTestClippedOutByBorder(
       rect.ToLayoutRect(), border_edges.line_left, border_edges.line_right));
 }
 
+bool NGBoxFragmentPainter::HitTestOverflowControl(
+    const HitTestContext& hit_test,
+    PhysicalOffset accumulated_offset) {
+  const auto* layout_box = ToLayoutBoxOrNull(box_fragment_.GetLayoutObject());
+  return layout_box &&
+         layout_box->HitTestOverflowControl(*hit_test.result, hit_test.location,
+                                            accumulated_offset);
+}
+
 }  // namespace blink

third_party/blink/renderer/core/paint/ng/ng_box_fragment_painter.h

@@ -272,6 +272,9 @@ class NGBoxFragmentPainter : public BoxPainterBase {
       const HitTestLocation&,
       const PhysicalOffset& border_box_location) const;
 
+  bool HitTestOverflowControl(const HitTestContext&,
+                              PhysicalOffset accumulated_offset);
+
   const NGPhysicalBoxFragment& PhysicalFragment() const {
     return box_fragment_;
   }