Add support for binary type data (ArrayBuffer)

Summary:
Entirely based on https://github.com/facebook/react-native/pull/1829
I just updated the diff to be compatible with the current master branch.
Closes https://github.com/facebook/react-native/pull/4483

Reviewed By: svcscm

Differential Revision: D2783425

Pulled By: nicklockwood

fb-gh-sync-id: 1cc67c0741cff3b071530877d688f6b8c1061e3f

Libraries/WebSocket/RCTWebSocketModule.m

@@ -76,8 +76,10 @@ RCT_EXPORT_METHOD(close:(nonnull NSNumber *)socketID)
 
 - (void)webSocket:(RCTSRWebSocket *)webSocket didReceiveMessage:(id)message
 {
+  BOOL binary = [message isKindOfClass:[NSData class]];
   [_bridge.eventDispatcher sendDeviceEventWithName:@"websocketMessage" body:@{
-    @"data": message,
+    @"data": binary ? [message base64EncodedStringWithOptions:0] : message,
+    @"type": binary ? @"binary" : @"text",
     @"id": webSocket.reactTag
   }];
 }