Support generic methods. Fix #556.

lib/src/argument_list_visitor.dart

Index: lib/src/argument_list_visitor.dart
diff --git a/lib/src/argument_list_visitor.dart b/lib/src/argument_list_visitor.dart
index 843d757aa0c0035284d6d9925b1750f857073fb6..38bc6eb04476037866aa374796e38a657a7885a7 100644
--- a/lib/src/argument_list_visitor.dart
+++ b/lib/src/argument_list_visitor.dart
@@ -153,9 +153,6 @@ class ArgumentListVisitor {
     // split before it, so try not to.
     if (_isSingle) _visitor.builder.startSpan();
 
-    // Nest around the parentheses in case there are comments before or after
-    // them.
-    _visitor.builder.nestExpression();
     _visitor.builder.startSpan();
     _visitor.token(_leftParenthesis);
 
@@ -193,8 +190,6 @@ class ArgumentListVisitor {
 
     _visitor.token(_rightParenthesis);
 
-    _visitor.builder.unnest();
-
     if (_isSingle) _visitor.builder.endSpan();
   }