tools: add buffer-constructor eslint rule

Now that the Buffer.alloc, allocUnsafe, and from methods have landed,
add a linting rule that requires their use within lib. Tests and
benchmarks are explicitly excluded by the rule.

PR-URL: #5740
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

lib/.eslintrc

@@ -1,3 +1,4 @@
 rules:
   # Custom rules in tools/eslint-rules
   require-buffer: 2
+  buffer-constructor: 2

src/.eslintrc

@@ -0,0 +1,3 @@
+rules:
+  # Custom rules in tools/eslint-rules
+  buffer-constructor: 2

tools/eslint-rules/buffer-constructor.js

@@ -0,0 +1,25 @@
+/**
+ * @fileoverview Require use of new Buffer constructor methods in lib
+ * @author James M Snell
+ */
+'use strict';
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+const msg = 'Use of the Buffer() constructor has been deprecated. ' +
+            'Please use either Buffer.alloc(), Buffer.allocUnsafe(), ' +
+            'or Buffer.from()';
+
+function test(context, node) {
+  if (node.callee.name === 'Buffer') {
+    context.report(node, msg);
+  }
+}
+
+module.exports = function(context) {
+  return {
+    'NewExpression': (node) => test(context, node),
+    'CallExpression': (node) => test(context, node)
+  };
+};