Improve IPC performance.

Reading of JSON data off the buffer, 10-15% performance increase.

Fixes #1864.

lib/child_process.js

@@ -77,14 +77,15 @@ function setupChannel(target, channel) {
     if (pool) {
       jsonBuffer += pool.toString('ascii', offset, offset + length);
 
-      var i;
-      while ((i = jsonBuffer.indexOf('\n')) >= 0) {
-        var json = jsonBuffer.slice(0, i);
+      var i, start = 0;
+      while ((i = jsonBuffer.indexOf('\n', start)) >= 0) {
+        var json = jsonBuffer.slice(start, i);
         var message = JSON.parse(json);
-        jsonBuffer = jsonBuffer.slice(i + 1);
 
         target.emit('message', message, recvHandle);
+        start = i+1;
       }
+      jsonBuffer = jsonBuffer.slice(start);
 
     } else {
       channel.close();