[LayoutNG] Bugfix: Can't hit NG scrollbars

Bug: 841587
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_layout_ng
Change-Id: I5454aa1fd7f48e4034b4379f5cd97ba17961c777
Reviewed-on: https://chromium-review.googlesource.com/1066929
Commit-Queue: Aleks Totic <atotic@chromium.org>
Reviewed-by: Xiaocheng Hu <xiaochengh@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#560227}

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

@@ -452,6 +452,11 @@ class CORE_EXPORT LayoutBlock : public LayoutBox {
 
   bool NeedsPreferredWidthsRecalculation() const override;
 
+  bool IsInSelfHitTestingPhase(HitTestAction hit_test_action) const final {
+    return hit_test_action == kHitTestBlockBackground ||
+           hit_test_action == kHitTestChildBlockBackground;
+  }
+
  private:
   LayoutObjectChildList* VirtualChildren() final { return Children(); }
   const LayoutObjectChildList* VirtualChildren() const final {
@@ -468,11 +473,6 @@ class CORE_EXPORT LayoutBlock : public LayoutBox {
   // Returns true if the positioned movement-only layout succeeded.
   bool TryLayoutDoingPositionedMovementOnly();
 
-  bool IsInSelfHitTestingPhase(HitTestAction hit_test_action) const final {
-    return hit_test_action == kHitTestBlockBackground ||
-           hit_test_action == kHitTestChildBlockBackground;
-  }
-
   bool IsPointInOverflowControl(HitTestResult&,
                                 const LayoutPoint& location_in_container,
                                 const LayoutPoint& accumulated_offset) const;

third_party/blink/renderer/core/layout/ng/layout_ng_mixin.cc

@@ -250,6 +250,10 @@ bool LayoutNGMixin<Base>::NodeAtPoint(
     if (!location_in_container.Intersects(overflow_box))
       return false;
   }
+  if (Base::IsInSelfHitTestingPhase(action) && Base::HasOverflowClip() &&
+      Base::HitTestOverflowControl(result, location_in_container,
+                                   adjusted_location))
+    return true;
 
   return NGBlockFlowPainter(*this).NodeAtPoint(result, location_in_container,
                                                accumulated_offset,