Debugger channel messages should be processed only on a background thread

Reviewed By: bnham

Differential Revision: D5470226

fbshipit-source-id: ccbc351e3f64f2baa8a3c74c5d0c67c44731bf32

Author: pakoito

React/Inspector/RCTInspectorPackagerConnection.m

@@ -18,6 +18,7 @@ @interface RCTInspectorPackagerConnection () <RCTSRWebSocketDelegate> {
   NSURL *_url;
   NSMutableDictionary<NSString *, RCTInspectorLocalConnection *> *_inspectorConnections;
   RCTSRWebSocket *_webSocket;
+  dispatch_queue_t _jsQueue;
   BOOL _closed;
   BOOL _suppressConnectionErrors;
 }
@@ -45,6 +46,7 @@ - (instancetype)initWithURL:(NSURL *)url
   if (self = [super init]) {
     _url = url;
     _inspectorConnections = [NSMutableDictionary new];
+    _jsQueue = dispatch_queue_create("com.facebook.react.WebSocketExecutor", DISPATCH_QUEUE_SERIAL);
   }
   return self;
 }
@@ -215,6 +217,7 @@ - (void)connect
   // timeouts, but it appears the iOS RCTSRWebSocket API doesn't have the same
   // implemented options.
   _webSocket = [[RCTSRWebSocket alloc] initWithURL:_url];
+  [_webSocket setDelegateDispatchQueue:_jsQueue];
   _webSocket.delegate = self;
   [_webSocket open];
 }