cppgc: Allow tracing using raw pointers

There are several use cases related to collections that require
tracing a raw pointer.

Bug: chromium:1056170
Change-Id: I162b5380e7bddd7be62cbc74aa0031c8695220a7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2643385Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72250}

include/cppgc/visitor.h

@@ -61,6 +61,22 @@ class V8_EXPORT Visitor {
 
   virtual ~Visitor() = default;
 
+  /**
+   * Trace method for raw pointers. Prefer the versions for managed pointers.
+   *
+   * \param member Reference retaining an object.
+   */
+  template <typename T>
+  void Trace(const T* t) {
+    static_assert(sizeof(T), "Pointee type must be fully defined.");
+    static_assert(internal::IsGarbageCollectedType<T>::value,
+                  "T must be GarbageCollected or GarbageCollectedMixin type");
+    if (!t) {
+      return;
+    }
+    Visit(t, TraceTrait<T>::GetTraceDescriptor(t));
+  }
+
   /**
    * Trace method for Member.
    *
@@ -287,17 +303,6 @@ class V8_EXPORT Visitor {
                   &HandleWeak<WeakPersistent>, &p, loc);
   }
 
-  template <typename T>
-  void Trace(const T* t) {
-    static_assert(sizeof(T), "Pointee type must be fully defined.");
-    static_assert(internal::IsGarbageCollectedType<T>::value,
-                  "T must be GarbageCollected or GarbageCollectedMixin type");
-    if (!t) {
-      return;
-    }
-    Visit(t, TraceTrait<T>::GetTraceDescriptor(t));
-  }
-
 #if V8_ENABLE_CHECKS
   void CheckObjectNotInConstruction(const void* address);
 #endif  // V8_ENABLE_CHECKS