cppgc-js: Fix leak in generating heap snapshots

StateBase requires a virtual destructor as it is destroyed through the
base class. Failing to provide a virtual dtor leaks internal state in
State (and possible in future RootState).

Bug: chromium:1056170
Change-Id: I4408a57dc05fdeb81408f571dd6eb87312ba7c9d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2964815Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75160}

src/heap/cppgc-js/cpp-snapshot.cc

@@ -106,6 +106,7 @@ class StateBase {
         visited_(visited) {
     DCHECK_NE(Visibility::kDependentVisibility, visibility);
   }
+  virtual ~StateBase() = default;
 
   // Visited objects have already been processed or are currently being
   // processed, see also IsPending() below.
@@ -189,6 +190,7 @@ class State final : public StateBase {
  public:
   State(const HeapObjectHeader& header, size_t state_count)
       : StateBase(&header, state_count, Visibility::kHidden, nullptr, false) {}
+  ~State() final = default;
 
   const HeapObjectHeader* header() const {
     return static_cast<const HeapObjectHeader*>(key_);
@@ -276,6 +278,7 @@ class RootState final : public StateBase {
   RootState(EmbedderRootNode* node, size_t state_count)
       // Root states are always visited, visible, and have a node attached.
       : StateBase(node, state_count, Visibility::kVisible, node, true) {}
+  ~RootState() final = default;
 };
 
 // Abstraction for storing states. Storage allows for creation and lookup of