Converting Scrollbar and ScrollableArea from EagerSweeping to PreFinalizer

Replaced Scrollbar destructor with equivalent prefinalizer.

Prefinalizer of ScrollableArea calls RunScrollCompleteCallbacks to
Release the callbacks, and resets uniqueptr to TaskRunnerTimer.

Bug: 981043
Change-Id: I45d35928eef440bc079de77364ac2d4d0ed6ecb1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1688968Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#675589}

third_party/blink/renderer/core/frame/visual_viewport.cc

@@ -1207,4 +1207,25 @@ std::unique_ptr<TracedValue> VisualViewport::ViewportToTracedValue() const {
   return value;
 }
 
+void VisualViewport::PreFinalize() {
+  root_transform_layer_.reset();
+  inner_viewport_container_layer_.reset();
+  overscroll_elasticity_layer_.reset();
+  page_scale_layer_.reset();
+  inner_viewport_scroll_layer_.reset();
+  // scrollbar_layer_group_* are referenced from overlay_scrollbar_*, thus
+  // overlay_scrollbar_* must be destroyed before scrollbar_layer_group_*.
+  overlay_scrollbar_horizontal_.reset();
+  overlay_scrollbar_vertical_.reset();
+  scrollbar_layer_group_horizontal_.reset();
+  scrollbar_layer_group_vertical_.reset();
+  device_emulation_transform_node_.reset();
+  overscroll_elasticity_transform_node_.reset();
+  scale_transform_node_.reset();
+  translation_transform_node_.reset();
+  scroll_node_.reset();
+  horizontal_scrollbar_effect_node_.reset();
+  vertical_scrollbar_effect_node_.reset();
+}
+
 }  // namespace blink

third_party/blink/renderer/core/frame/visual_viewport.h

@@ -274,6 +274,8 @@ class CORE_EXPORT VisualViewport final
   void SetNeedsPaintPropertyUpdate() { needs_paint_property_update_ = true; }
   bool NeedsPaintPropertyUpdate() const { return needs_paint_property_update_; }
 
+  void PreFinalize() override;
+
  private:
   bool DidSetScaleOrLocation(float scale,
                              bool is_pinch_gesture_active,

third_party/blink/renderer/core/paint/paint_layer_scrollable_area.cc

@@ -2912,4 +2912,10 @@ bool PaintLayerScrollableArea::ScrollingBackgroundDisplayItemClient::
       ->PaintedOutputOfObjectHasNoEffectRegardlessOfSize();
 }
 
+void PaintLayerScrollableArea::PreFinalize() {
+  if (!HasBeenDisposed())
+    Dispose();
+  rare_data_.reset();
+}
+
 }  // namespace blink

third_party/blink/renderer/core/paint/paint_layer_scrollable_area.h

@@ -551,6 +551,8 @@ class CORE_EXPORT PaintLayerScrollableArea final
     return scrolling_background_display_item_client_;
   }
 
+  void PreFinalize() override;
+  
  private:
   bool NeedsScrollbarReconstruction() const;
 

third_party/blink/renderer/core/scroll/scroll_animator_test.cc

@@ -139,6 +139,10 @@ class MockScrollableAreaForAnimatorTest
     ScrollableArea::Trace(visitor);
   }
 
+  virtual void PreFinalize() {
+      timer_task_runner_.reset();
+  }
+
  private:
   bool scroll_animator_enabled_;
   ScrollOffset min_offset_;

third_party/blink/renderer/core/scroll/scrollable_area.cc

@@ -93,10 +93,16 @@ ScrollableArea::ScrollableArea()
       needs_show_scrollbar_layers_(false),
       uses_composited_scrolling_(false) {}
 
-ScrollableArea::~ScrollableArea() {
+ScrollableArea::~ScrollableArea() = default;
+
+void ScrollableArea::Dispose() {
   RunScrollCompleteCallbacks();
+  fade_overlay_scrollbars_timer_.reset();
+  PreFinalize();
 }
 
+void ScrollableArea::PreFinalize() {}
+
 void ScrollableArea::ClearScrollableArea() {
 #if defined(OS_MACOSX)
   if (scroll_animator_)

third_party/blink/renderer/core/scroll/scrollable_area.h

@@ -67,6 +67,7 @@ enum IncludeScrollbarsInRect {
 
 class CORE_EXPORT ScrollableArea : public GarbageCollectedMixin {
   DISALLOW_COPY_AND_ASSIGN(ScrollableArea);
+  USING_PRE_FINALIZER(ScrollableArea, Dispose);
 
  public:
   using ScrollCallback = base::OnceClosure;
@@ -349,6 +350,9 @@ class CORE_EXPORT ScrollableArea : public GarbageCollectedMixin {
 
   virtual ~ScrollableArea();
 
+  void Dispose();
+  virtual void PreFinalize();
+
   // Called when any of horizontal scrollbar, vertical scrollbar and scroll
   // corner is setNeedsPaintInvalidation.
   virtual void ScrollControlWasSetNeedsPaintInvalidation() = 0;
@@ -389,8 +393,6 @@ class CORE_EXPORT ScrollableArea : public GarbageCollectedMixin {
   // for layout movements (bit.ly/scroll-anchoring).
   virtual bool ShouldPerformScrollAnchoring() const { return false; }
 
-  // Need to promptly let go of owned animator objects.
-  EAGERLY_FINALIZE();
   void Trace(blink::Visitor*) override;
 
   virtual void ClearScrollableArea();

third_party/blink/renderer/core/scroll/scrollbar.cc

@@ -83,7 +83,9 @@ Scrollbar::Scrollbar(ScrollableArea* scrollable_area,
   current_pos_ = ScrollableAreaCurrentPos();
 }
 
-Scrollbar::~Scrollbar() {
+Scrollbar::~Scrollbar() =default;
+
+void Scrollbar::Dispose() {
   theme_.UnregisterScrollbar(*this);
 }
 

third_party/blink/renderer/core/scroll/scrollbar.h

@@ -47,6 +47,7 @@ class WebMouseEvent;
 
 class CORE_EXPORT Scrollbar : public GarbageCollectedFinalized<Scrollbar>,
                               public DisplayItemClient {
+    USING_PRE_FINALIZER(Scrollbar, Dispose);
  public:
   // Theme object ownership remains with the caller and it must outlive the
   // scrollbar.
@@ -191,7 +192,7 @@ class CORE_EXPORT Scrollbar : public GarbageCollectedFinalized<Scrollbar>,
 
   // Promptly unregister from the theme manager + run finalizers of derived
   // Scrollbars.
-  EAGERLY_FINALIZE();
+  void Dispose();
   virtual void Trace(blink::Visitor*);
 
  protected: