Remove the check for externally owned Future in IsSafeToDelete()

It is safe to delete ReferenceCountedFutureImpl even if there is any externally owned Future because the future will be invalidated by CleanupNotifier in ~ReferenceCountedFutureImpl().

PiperOrigin-RevId: 261033497

Author: chkuang-g

app/src/reference_counted_future_impl.cc

@@ -490,25 +490,11 @@ void ReferenceCountedFutureImpl::SetCompletionCallbackLambda(
 bool ReferenceCountedFutureImpl::IsSafeToDelete() const {
   MutexLock lock(mutex_);
   // Check if any Futures we have are still pending.
-  int total_references = 0;
-  int internal_references = 0;
   for (auto i = backings_.begin(); i != backings_.end(); ++i) {
     // If any Future is still pending, not safe to delete.
     if (i->second->status == kFutureStatusPending) return false;
-    // Count the total number of references to all valid Futures.
-    total_references += i->second->reference_count;
   }
-  for (int i = 0; i < last_results_.size(); i++) {
-    if (last_results_[i].status() != kFutureStatusInvalid) {
-      // If the status is not invalid, this entry is using up a reference.
-      // Count up the internal references.
-      internal_references++;
-    }
-  }
-  // If the only references are internal references, we're safe to delete.
-  // Otherwise, someone somewhere is holding onto a Future, and it's not
-  // yet safe to delete.
-  return total_references == internal_references;
+  return true;
 }
 
 void ReferenceCountedFutureImpl::SetContextData(

app/src/reference_counted_future_impl.h

@@ -366,8 +366,7 @@ class ReferenceCountedFutureImpl : public detail::FutureApiInterface {
   size_t GetLastResultCount() { return last_results_.size(); }
 
   /// Check if it's safe to delete this API. It's only safe to delete this if
-  /// no futures are Pending, and if there are no references to Futures other
-  /// than in last_results_.
+  /// no futures are Pending.
   bool IsSafeToDelete() const;
 
   /// Sets temporary context data associated with a FutureHandle that will be