Introduce NGPaintFragment::RareData

This patch Introduces |NGPaintFragment::RareData()| to reduce memory usage
of |NGPaintFragment|.

Change-Id: I4b74f1b0cddcbb432b84847173f93bb4c897d08d
Reviewed-on: https://chromium-review.googlesource.com/c/1343810Reviewed-by: Koji Ishii <kojii@chromium.org>
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609893}

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

@@ -39,7 +39,7 @@ struct SameSizeAsNGPaintFragment : public RefCounted<NGPaintFragment>,
                                    public ImageResourceObserver {
   void* pointers[6];
   NGPhysicalOffset offsets[2];
-  LayoutRect rects[2];
+  LayoutRect rects[1];
   unsigned flags;
 };
 
@@ -302,6 +302,12 @@ scoped_refptr<NGPaintFragment> NGPaintFragment::Create(
   return paint_fragment;
 }
 
+NGPaintFragment::RareData& NGPaintFragment::EnsureRareData() {
+  if (!rare_data_)
+    rare_data_ = std::make_unique<RareData>();
+  return *rare_data_;
+}
+
 void NGPaintFragment::UpdateFromCachedLayoutResult(
     scoped_refptr<const NGPhysicalFragment> fragment,
     NGPhysicalOffset offset) {
@@ -329,16 +335,22 @@ void NGPaintFragment::UpdateFromCachedLayoutResult(
 
 NGPaintFragment* NGPaintFragment::Last(const NGBreakToken& break_token) {
   for (NGPaintFragment* fragment = this; fragment;
-       fragment = fragment->next_fragmented_.get()) {
+       fragment = fragment->Next()) {
     if (fragment->PhysicalFragment().BreakToken() == &break_token)
       return fragment;
   }
   return nullptr;
 }
 
+NGPaintFragment* NGPaintFragment::Next() {
+  if (!rare_data_)
+    return nullptr;
+  return rare_data_->next_fragmented_.get();
+}
+
 NGPaintFragment* NGPaintFragment::Last() {
   for (NGPaintFragment* fragment = this;;) {
-    NGPaintFragment* next = fragment->next_fragmented_.get();
+    NGPaintFragment* next = fragment->Next();
     if (!next)
       return fragment;
     fragment = next;
@@ -360,7 +372,8 @@ scoped_refptr<NGPaintFragment>* NGPaintFragment::Find(
     if (!*fragment)
       return fragment;
 
-    scoped_refptr<NGPaintFragment>* next = &(*fragment)->next_fragmented_;
+    scoped_refptr<NGPaintFragment>* next =
+        &(*fragment)->EnsureRareData().next_fragmented_;
     if ((*fragment)->PhysicalFragment().BreakToken() == break_token)
       return next;
     fragment = next;
@@ -369,7 +382,9 @@ scoped_refptr<NGPaintFragment>* NGPaintFragment::Find(
 }
 
 void NGPaintFragment::SetNext(scoped_refptr<NGPaintFragment> fragment) {
-  next_fragmented_ = std::move(fragment);
+  if (!rare_data_ && !fragment)
+    return;
+  EnsureRareData().next_fragmented_ = std::move(fragment);
 }
 
 bool NGPaintFragment::IsDescendantOfNotSelf(
@@ -397,6 +412,18 @@ bool NGPaintFragment::ShouldClipOverflow() const {
          ToNGPhysicalBoxFragment(*physical_fragment_).ShouldClipOverflow();
 }
 
+LayoutRect NGPaintFragment::SelectionVisualRect() const {
+  if (!rare_data_)
+    return LayoutRect();
+  return rare_data_->selection_visual_rect_;
+}
+
+void NGPaintFragment::SetSelectionVisualRect(const LayoutRect& rect) {
+  if (!rare_data_ && rect.IsEmpty())
+    return;
+  EnsureRareData().selection_visual_rect_ = rect;
+}
+
 LayoutRect NGPaintFragment::SelfInkOverflow() const {
   return physical_fragment_->InkOverflow().ToLayoutRect();
 }

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

@@ -58,7 +58,7 @@ class CORE_EXPORT NGPaintFragment : public RefCounted<NGPaintFragment>,
       NGPhysicalOffset offset);
 
   // Next/last fragment for  when this is fragmented.
-  NGPaintFragment* Next() { return next_fragmented_.get(); }
+  NGPaintFragment* Next();
   void SetNext(scoped_refptr<NGPaintFragment>);
   NGPaintFragment* Last();
   NGPaintFragment* Last(const NGBreakToken&);
@@ -170,10 +170,8 @@ class CORE_EXPORT NGPaintFragment : public RefCounted<NGPaintFragment>,
   LayoutRect VisualRect() const override { return visual_rect_; }
   void SetVisualRect(const LayoutRect& rect) { visual_rect_ = rect; }
 
-  LayoutRect SelectionVisualRect() const { return selection_visual_rect_; }
-  void SetSelectionVisualRect(const LayoutRect& rect) {
-    selection_visual_rect_ = rect;
-  }
+  LayoutRect SelectionVisualRect() const;
+  void SetSelectionVisualRect(const LayoutRect& rect);
 
   // CSS ink overflow https://www.w3.org/TR/css-overflow-3/#ink
   // Encloses all pixels painted by self + children.
@@ -334,8 +332,18 @@ class CORE_EXPORT NGPaintFragment : public RefCounted<NGPaintFragment>,
   scoped_refptr<NGPaintFragment> first_child_;
   scoped_refptr<NGPaintFragment> next_sibling_;
 
-  // The next fragment for when this is fragmented.
-  scoped_refptr<NGPaintFragment> next_fragmented_;
+  struct RareData {
+    USING_FAST_MALLOC(RareData);
+
+   public:
+    // The next fragment for when this is fragmented.
+    scoped_refptr<NGPaintFragment> next_fragmented_;
+
+    // Used for invalidating selected fragment.
+    LayoutRect selection_visual_rect_;
+  };
+  RareData& EnsureRareData();
+  std::unique_ptr<RareData> rare_data_;
 
   NGPaintFragment* next_for_same_layout_object_ = nullptr;
   NGPhysicalOffset inline_offset_to_container_box_;
@@ -351,7 +359,6 @@ class CORE_EXPORT NGPaintFragment : public RefCounted<NGPaintFragment>,
   //
 
   LayoutRect visual_rect_;
-  LayoutRect selection_visual_rect_;
 };
 
 extern template class CORE_EXTERN_TEMPLATE_EXPORT