Make hit test on culled inline faster

This patch changes |LayoutInlineCollector| to use |IsDescendantOf()| instead of
using |HashSet<T>| to make |SelftFragmentsOf()|, which is used by hit testing
and others, faster.

I found the slowness of |LayoutInlineCollector| by CPU profiling[1] where
|HashSet<T>::insert()| consumes most of time.

So, it seems traversing fragment tree + LayoutObject::IsDescendnatOf()| is
faster than two times of traversing fragment tree + |HashSet<T>::insert()|.


[1] https://bit.ly/2pXQbcE

Bug: 1008523
Change-Id: I825197f2b85fd2ef573e8ff159ddf966489361be
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1847602
Auto-Submit: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Koji Ishii <kojii@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#704102}

third_party/blink/renderer/core/layout/ng/inline/ng_inline_fragment_traversal.cc

@@ -122,9 +122,8 @@ class LayoutInlineCollector final : public NGPhysicalFragmentCollectorBase {
   STACK_ALLOCATED();
 
  public:
-  explicit LayoutInlineCollector(const LayoutInline& container) {
-    CollectInclusiveDescendants(container);
-  }
+  explicit LayoutInlineCollector(const LayoutInline& container)
+      : container_(container) {}
 
   Vector<Result> CollectFrom(const NGPhysicalFragment& fragment) final {
     return CollectExclusivelyFrom(fragment);
@@ -133,30 +132,14 @@ class LayoutInlineCollector final : public NGPhysicalFragmentCollectorBase {
  private:
   void Visit() final {
     if (!GetFragment().IsLineBox() &&
-        inclusive_descendants_.Contains(GetFragment().GetLayoutObject())) {
+        GetFragment().GetLayoutObject()->IsDescendantOf(&container_)) {
       Emit();
       return;
     }
     VisitChildren();
   }
 
-  void CollectInclusiveDescendants(const LayoutInline& container) {
-    inclusive_descendants_.insert(&container);
-    for (const LayoutObject* node = container.FirstChild(); node;
-         node = node->NextSibling()) {
-      if (node->IsFloatingOrOutOfFlowPositioned())
-        continue;
-      if (node->IsBox() || node->IsText()) {
-        inclusive_descendants_.insert(node);
-        continue;
-      }
-      if (!node->IsLayoutInline())
-        continue;
-      CollectInclusiveDescendants(ToLayoutInline(*node));
-    }
-  }
-
-  HashSet<const LayoutObject*> inclusive_descendants_;
+  const LayoutInline& container_;
 
   DISALLOW_COPY_AND_ASSIGN(LayoutInlineCollector);
 };