partially implement instance of checks and some codegen fixes

lib/src/js/printer.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of js_ast;
 
 
 class JavaScriptPrintingOptions {
   final bool shouldCompressOutput;
   final bool minifyLocalVariables;
@@ skipping 598 matching lines @@
                           newInForInit: false, newAtStatementBegin: false);
     spaceOut();
     out(":");
     spaceOut();
     visitNestedExpression(cond.otherwise, ASSIGNMENT,
                           newInForInit: inForInit, newAtStatementBegin: false);
   }
 
   visitNew(New node) {
     out("new ");
-    visitNestedExpression(node.target, CALL,
+    visitNestedExpression(node.target, ACCESS,

[Jennifer Messerly, 2015/04/01 00:32:35]

this is important in ES6 at least:

`new foo()()` won't work
`new (foo())()` will

                           newInForInit: inForInit, newAtStatementBegin: false);
     out("(");
     visitCommaSeparated(node.arguments, ASSIGNMENT,
                         newInForInit: false, newAtStatementBegin: false);
     out(")");
   }
 
   visitCall(Call call) {
     visitNestedExpression(call.target, LEFT_HAND_SIDE,
                           newInForInit: inForInit,
@@ skipping 735 matching lines @@
         codes.add(nthLetter((n ~/ nameSpaceSize) % LETTERS));
       }
       codes.add(charCodes.$0 + digit);
       newName = new String.fromCharCodes(codes);
     }
     assert(new RegExp(r'[a-zA-Z][a-zA-Z0-9]*').hasMatch(newName));
     maps.last[oldName] = newName;
     return newName;
   }
 }