stream: removed unecessary writing property

writecb casted to boolean has the same
value as writing.

lib/_stream_writable.js

@@ -120,9 +120,6 @@ function WritableState(options, stream, isDuplex) {
   // socket or file.
   this.length = 0;
 
-  // A flag to see when we're in the middle of a write.
-  this.writing = false;
-
   // When true all writes will be buffered until .uncork() call
   this.corked = 0;
 
@@ -188,6 +185,14 @@ function WritableState(options, stream, isDuplex) {
   this.corkedRequestsFree = corkReq;
 }
 
+ObjectDefineProperties(WritableState.prototype, {
+  writing: {
+    get() {
+      return !!this.writecb;
+    }
+  }
+});
+
 WritableState.prototype.getBuffer = function getBuffer() {
   let current = this.bufferedRequest;
   const out = [];
@@ -318,7 +323,7 @@ Writable.prototype.uncork = function() {
   if (state.corked) {
     state.corked--;
 
-    if (!state.writing &&
+    if (!state.writecb &&
         !state.corked &&
         !state.bufferProcessing &&
         state.bufferedRequest)
@@ -349,7 +354,7 @@ function writeOrBuffer(stream, state, chunk, encoding, cb) {
   if (!ret)
     state.needDrain = true;
 
-  if (state.writing || state.corked || state.errored) {
+  if (state.writecb || state.corked || state.errored) {
     const last = state.lastBufferedRequest;
     state.lastBufferedRequest = {
       chunk,
@@ -375,7 +380,6 @@ function writeOrBuffer(stream, state, chunk, encoding, cb) {
 function doWrite(stream, state, writev, len, chunk, encoding, cb) {
   state.writelen = len;
   state.writecb = cb;
-  state.writing = true;
   state.sync = true;
   if (state.destroyed)
     state.onwrite(new ERR_STREAM_DESTROYED('write'));
@@ -409,7 +413,6 @@ function onwrite(stream, er) {
     return;
   }
 
-  state.writing = false;
   state.writecb = null;
   state.length -= state.writelen;
   state.writelen = 0;
@@ -484,7 +487,7 @@ function afterWrite(stream, state, count, cb) {
 
 // If there's something in the buffer waiting, then invoke callbacks.
 function errorBuffer(state, err) {
-  if (state.writing || !state.bufferedRequest) {
+  if (state.writecb || !state.bufferedRequest) {
     return;
   }
 
@@ -551,7 +554,7 @@ function clearBuffer(stream, state) {
       // it means that we need to wait until it does.
       // also, that means that the chunk and cb are currently
       // being processed, so move the buffer counter past them.
-      if (state.writing) {
+      if (state.writecb) {
         break;
       }
     }
@@ -621,7 +624,7 @@ function needFinish(state) {
           !state.errored &&
           state.bufferedRequest === null &&
           !state.finished &&
-          !state.writing);
+          !state.writecb);
 }
 
 function callFinal(stream, state) {