buffer: Fixing deopt when constructed with strings

When a buffer was created using `new Buffer('A String')`, internally within the buffer class we would read arguments[1], however in this case we would be reading outside of the array causing a deopt to occur. This fixes this issue by casting the type to a string before use, and removing the usage of the arguments object.

Author: tomgco

lib/buffer.js

@@ -40,7 +40,7 @@ function alignPool() {
 }
 
 
-function Buffer(arg) {
+function Buffer(arg, encoding) {
  // Common case.
  if (typeof arg === 'number') {
  // If less than zero, or NaN.
@@ -51,7 +51,11 @@ function Buffer(arg) {
 
  // Slightly less common case.
  if (typeof arg === 'string') {
- return fromString(arg, arguments[1]);
+ encoding = encoding || '';
+ if (typeof encoding !== 'string' || encoding === '')
+ encoding = 'utf8';
+
+ return fromString(arg, encoding);
  }
 
  // Unusual.
@@ -103,9 +107,6 @@ function allocate(size) {
 
 
 function fromString(string, encoding) {
- if (typeof encoding !== 'string' || encoding === '')
- encoding = 'utf8';
-
  var length = byteLength(string, encoding);
  if (length >= (Buffer.poolSize >>> 1))
  return binding.createFromString(string, encoding);