cppgc: Check for wrong sentinel values

Check for the most commonly used wrong sentinel value (-1). Users
should use cppgc::kSentinelPointer instead.

Bug: chromium:1263009
Change-Id: I200954bcd70c6a100ffec24aece3e1843e1438a0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3242002
Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77529}

src/heap/cppgc/pointer-policies.cc

@@ -34,6 +34,8 @@ void SameThreadEnabledCheckingPolicyBase::CheckPointerImpl(
     const void* ptr, bool points_to_payload, bool check_off_heap_assignments) {
   // `ptr` must not reside on stack.
   DCHECK(!IsOnStack(ptr));
+  // Check for the most commonly used wrong sentinel value (-1).
+  DCHECK_NE(reinterpret_cast<void*>(-1), ptr);
   auto* base_page = BasePage::FromPayload(ptr);
   // Large objects do not support mixins. This also means that `base_page` is
   // valid for large objects.