Disable eager tracing for NGPhysicalFragment.

third_party/WebKit/Source/core/layout/ng/ng_physical_fragment.h

Index: third_party/WebKit/Source/core/layout/ng/ng_physical_fragment.h
diff --git a/third_party/WebKit/Source/core/layout/ng/ng_physical_fragment.h b/third_party/WebKit/Source/core/layout/ng/ng_physical_fragment.h
index b225795d24ae998e14aba5f93b84c2a6bce0519a..28ad7cb8d1c4b38fc4681bf0c81d0e83fa581bb1 100644
--- a/third_party/WebKit/Source/core/layout/ng/ng_physical_fragment.h
+++ b/third_party/WebKit/Source/core/layout/ng/ng_physical_fragment.h
@@ -37,6 +37,8 @@ class CORE_EXPORT NGPhysicalFragment final : public NGPhysicalFragmentBase {
   HeapVector<Member<const NGPhysicalFragmentBase>> children_;
 };
 
+WILL_NOT_BE_EAGERLY_TRACED_CLASS(NGPhysicalFragment);
+
 }  // namespace blink
 
 #endif  // NGPhysicalFragment_h