[dart:io] Adds a finalizer to _NativeSocket to avoid socket leaks

runtime/bin/eventhandler_fuchsia.cc

Index: runtime/bin/eventhandler_fuchsia.cc
diff --git a/runtime/bin/eventhandler_fuchsia.cc b/runtime/bin/eventhandler_fuchsia.cc
index 438d36eb1efa60c90873dcfeda05807a3b4756d9..3d586ca034995a3f1ce01d1943768d7253d5d24b 100644
--- a/runtime/bin/eventhandler_fuchsia.cc
+++ b/runtime/bin/eventhandler_fuchsia.cc
@@ -279,8 +279,13 @@ void EventHandlerImplementation::HandleInterruptFd() {
     } else {
       ASSERT((msg[i].data & COMMAND_MASK) != 0);
       LOG_INFO("HandleInterruptFd command\n");
+      Socket* socket = reinterpret_cast<Socket*>(msg[i].id);
+      RefCntReleaseScope<Socket> rs(socket);
+      if (socket->fd() == -1) {
+        continue;
+      }
       DescriptorInfo* di =
-          GetDescriptorInfo(msg[i].id, IS_LISTENING_SOCKET(msg[i].data));
+          GetDescriptorInfo(socket->fd(), IS_LISTENING_SOCKET(msg[i].data));
       if (IS_COMMAND(msg[i].data, kShutdownReadCommand)) {
         ASSERT(!di->IsListeningSocket());
         // Close the socket for reading.
@@ -311,13 +316,14 @@ void EventHandlerImplementation::HandleInterruptFd() {
 
           MutexLocker locker(registry->mutex());
 
-          if (registry->CloseSafe(fd)) {
+          if (registry->CloseSafe(socket)) {
             ASSERT(new_mask == 0);
             socket_map_.Remove(GetHashmapKeyFromFd(fd),
                                GetHashmapHashFromFd(fd));
             di->Close();
             LOG_INFO("Closed %d\n", di->fd());
             delete di;
+            socket->SetClosedFd();
           }
         } else {
           ASSERT(new_mask == 0);
@@ -325,6 +331,7 @@ void EventHandlerImplementation::HandleInterruptFd() {
           di->Close();
           LOG_INFO("Closed %d\n", di->fd());
           delete di;
+          socket->SetClosedFd();
         }
 
         bool success = DartUtils::PostInt32(port, 1 << kDestroyedEvent);
@@ -468,6 +475,7 @@ void EventHandlerImplementation::Poll(uword args) {
       handler_impl->HandleEvents(events, result);
     }
   }
+  DEBUG_ASSERT(ReferenceCounted<Socket>::instances() == 0);
   handler->NotifyShutdownDone();
 }