stream: resolve perf regression introduced by V8 7.3

lib/_stream_readable.js

@@ -256,7 +256,8 @@ function readableAddChunk(stream, chunk, encoding, addToFront) {
     } else if (state.objectMode || chunk && chunk.length > 0) {
       if (typeof chunk !== 'string' &&
           !state.objectMode &&
-          Object.getPrototypeOf(chunk) !== Buffer.prototype) {
+          // Do not use Object.getPrototypeOf as it is slower.
+          !(chunk instanceof Buffer)) {
         chunk = Stream._uint8ArrayToBuffer(chunk);
       }
 
@@ -399,7 +400,13 @@ function howMuchToRead(n, state) {
 // You can override either this method, or the async _read(n) below.
 Readable.prototype.read = function(n) {
   debug('read', n);
-  n = parseInt(n, 10);
+  // Same as parseInt(undefined, 10), however V8 7.3 performance regressed
+  // in this scenario, so we are doing it manually.
+  if (n === undefined) {
+    n = NaN;
+  } else if (!Number.isInteger(n)) {
+    n = parseInt(n, 10);
+  }
   const state = this._readableState;
   const nOrig = n;
 

lib/_stream_writable.js

@@ -277,7 +277,8 @@ Writable.prototype.write = function(chunk, encoding, cb) {
   var ret = false;
   const isBuf = !state.objectMode && Stream._isUint8Array(chunk);
 
-  if (isBuf && Object.getPrototypeOf(chunk) !== Buffer.prototype) {
+  // Do not use Object.getPrototypeOf as it is slower since V8 7.3.
+  if (isBuf && !(chunk instanceof Buffer)) {
     chunk = Stream._uint8ArrayToBuffer(chunk);
   }