stream: prevent object map change in ReadableState

ReadableState has the resumeScheduled property that helps determine if
a stream should be resumed. It was not assigned in the constructor.
When stream.resume is called on a readable stream that is not flowing,
it is set to true. This changes the property map of the ReadableState
which can cause a deopt in onEofChunk and needMoreData.

PR-URL: #4761
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Brian White <mscdex@mscdex.net>

lib/_stream_readable.js

@@ -51,6 +51,7 @@ function ReadableState(options, stream) {
   this.needReadable = false;
   this.emittedReadable = false;
   this.readableListening = false;
+  this.resumeScheduled = false;
 
   // Crypto is kind of old and crusty.  Historically, its default string
   // encoding is 'binary' so we have to make this configurable.