[fuchsia] Handle Frame disconnected case in NamedMessagePortConnector.

Calling the RemoveBeforeLoadJavaScript() function on a Frame that has
already disconnected is benign, but triggers warning logspam, so handle
the case of deletion after Frame disconnection gracefully.

Bug: b/150973463
Change-Id: Ia029a561221bf05d1f8500a5a502e6c06841e07b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2095725
Auto-Submit: Wez <wez@chromium.org>
Commit-Queue: Kevin Marshall <kmarshall@chromium.org>
Reviewed-by: Kevin Marshall <kmarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#749311}

fuchsia/runners/cast/named_message_port_connector.cc

@@ -51,8 +51,12 @@ NamedMessagePortConnector::NamedMessagePortConnector(fuchsia::web::Frame* frame)
 }
 
 NamedMessagePortConnector::~NamedMessagePortConnector() {
-  frame_->RemoveBeforeLoadJavaScript(static_cast<uint64_t>(
-      CastPlatformBindingsId::NAMED_MESSAGE_PORT_CONNECTOR));
+  if (frame_) {
+    // Don't attempt to remove before-load JavaScript when being deleted because
+    // the Frame has disconnected.
+    frame_->RemoveBeforeLoadJavaScript(static_cast<uint64_t>(
+        CastPlatformBindingsId::NAMED_MESSAGE_PORT_CONNECTOR));
+  }
 }
 
 void NamedMessagePortConnector::Register(DefaultPortConnectedCallback handler) {