Create LayoutShiftTracker::ContainingBlockScope for the first fragment only

Currently PaintInvalidator iterates all block fragments with one context
for each LayoutObject, so we should create ContainingBlockScope only once
for the first fragment only. Previously creating multiple
ContainingBlockScopes for one multi-block-fragment object broke stacking
of the scopes, causing memory corruption.

Add check in ~ContainingBlockScope for stacking error in the scopes.

This limitation will be removed with LayoutNGFragmentTraversal which
traverses block fragments in depth-first order.

Bug: 1113710
Change-Id: I07aa3626f1a1d34714459e256880a96897585d4c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2339449Reviewed-by: Philip Rogers <pdr@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#796093}

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

@@ -84,6 +84,9 @@ class CORE_EXPORT LayoutShiftTracker final
     explicit ReattachHookScope(const Node&);
     ~ReattachHookScope();
 
+    ReattachHookScope(const ReattachHookScope&) = delete;
+    ReattachHookScope& operator=(const ReattachHookScope&) = delete;
+
     static void NotifyDetach(const Node&);
     static void NotifyAttach(const Node&);
 
@@ -117,7 +120,13 @@ class CORE_EXPORT LayoutShiftTracker final
           new_rect_(new_rect) {
       top_ = this;
     }
-    ~ContainingBlockScope() { top_ = outer_; }
+    ~ContainingBlockScope() {
+      DCHECK_EQ(top_, this);
+      top_ = outer_;
+    }
+
+    ContainingBlockScope(const ContainingBlockScope&) = delete;
+    ContainingBlockScope& operator=(const ContainingBlockScope&) = delete;
 
    private:
     friend class LayoutShiftTracker;

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

@@ -237,6 +237,9 @@ void PaintInvalidator::UpdateLayoutShiftTracking(
   }();
 
   bool should_create_containing_block_scope =
+      // TODO(crbug.com/1104064): Support multiple-fragments when switching to
+      // LayoutNGFragmentTraversal.
+      context.fragment_data == &box.FirstFragment() &&
       box.IsLayoutBlockFlow() && box.ChildrenInline() && box.SlowFirstChild();
   if (!should_report_layout_shift && !should_create_containing_block_scope)
     return;