cppgc: Fix new/delete mismatch in heap snapshot generation

Before this CL the C strings were generated using new char[] and
destroyed using delete. Fix this by avoiding a raw new[] call and
directly using unique_ptr.

Bug: chromium:1056170
Change-Id: I894171d58a3f7a765cdf86e07d3da2e9298a4a92
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2960275Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75147}

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

@@ -63,10 +63,10 @@ class EmbedderNode : public v8::EmbedderGraph::Node {
   // embedder until the snapshot is compiled.
   const char* InternalizeEdgeName(std::string edge_name) {
     const size_t edge_name_len = edge_name.length();
-    char* raw_edge_name_str = new char[edge_name_len + 1];
-    snprintf(raw_edge_name_str, edge_name_len + 1, "%s", edge_name.c_str());
-    named_edges_.emplace_back(raw_edge_name_str);
-    return named_edges_.back().get();
+    named_edges_.emplace_back(std::make_unique<char[]>(edge_name_len + 1));
+    char* named_edge_str = named_edges_.back().get();
+    snprintf(named_edge_str, edge_name_len + 1, "%s", edge_name.c_str());
+    return named_edge_str;
   }
 
  private:
@@ -74,7 +74,7 @@ class EmbedderNode : public v8::EmbedderGraph::Node {
   size_t size_;
   Node* wrapper_node_ = nullptr;
   Detachedness detachedness_ = Detachedness::kUnknown;
-  std::vector<std::unique_ptr<const char>> named_edges_;
+  std::vector<std::unique_ptr<char[]>> named_edges_;
 };
 
 // Node representing an artificial root group, e.g., set of Persistent handles.