dart2js: Refactoring, documentation, and a few bugfixes in Namer class.

tests/compiler/dart2js/pretty_parameter_test.dart

 // Copyright (c) 2011, 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.
 // Test that parameters keep their names in the output.
 
 import 'dart:async';
 import 'package:expect/expect.dart';
 import 'package:async_helper/async_helper.dart';
 import 'compiler_helper.dart';
 
@@ skipping 61 matching lines @@
 }
 """;
 
 main() {
   asyncTest(() => Future.wait([
     compile(FOO, entry: 'foo', check: (String generated) {
       Expect.isTrue(generated.contains(r"function(a, b) {"));
     }),
 
     compile(BAR, entry: 'bar', check: (String generated) {
-      Expect.isTrue(generated.contains(r"function($eval, $$eval) {"));
+      Expect.isTrue(generated.contains(r"function($eval, $eval0) {"));

[sra1, 2015/01/30 22:48:27]

Can we do something to keep the original names where possible?
(eval, $eval)
-->
($eval, $eval0)
This is confusing when you have to step through the generated code.

[asgerf, 2015/02/03 17:39:14]

Do you mean "original names" as in, the names from the source code? Or the names
that the Namer would use before the refactoring?

Previously it was (eval,$eval) -> ($eval, $$eval)
Now it's (eval,$eval) -> ($eval, $eval0)

Neither of them preserved the variable's original name.

If it's important I can make it use $$eval instead of $eval0, but it does not
seem that much better to me.

     }),
 
     compile(PARAMETER_AND_TEMP, entry: 'bar', check: (String generated) {
       Expect.isTrue(generated.contains(r"print(t00)"));
       // Check that the second 't0' got another name.
       Expect.isTrue(generated.contains(r"print(t01)"));
     }),
 
     compile(MULTIPLE_PHIS_ONE_LOCAL, entry: 'foo', check: (String generated) {
       Expect.isTrue(generated.contains("var a;"));
       // Check that there is only one var declaration.
       checkNumberOfMatches(new RegExp("var").allMatches(generated).iterator, 1);
     }),
 
     compile(NO_LOCAL, entry: 'foo', check: (String generated) {
       Expect.isFalse(generated.contains('var'));
     }),
 
     compile(PARAMETER_INIT, entry: 'foo', check: (String generated) {
       // Check that there is only one var declaration.
       checkNumberOfMatches(new RegExp("var").allMatches(generated).iterator, 1);
     }),
   ]));
 }