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

tests/language/named_parameter_clash_test.dart

+// Copyright (c) 2015, 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.
+
+import 'package:expect/expect.dart';
+
+class Foo {
+  m({a, b, c}) {
+    try {} catch(e) {} // no inline
+    return 'Foo $a $b $c';
+  }
+}
+
+class Bar {
+  m(z, {a$b, c}) {
+    try {} catch(e) {} // no inline
+    var ab = a$b;
+    return 'Bar $z $ab $c';
+  }
+}
+
+inscrutable(xs, i) => i == 0 ? xs[0] : inscrutable(xs.sublist(1), i-1);
+
+main() {
+  var list = [new Foo(), new Bar()];
+  var foo = inscrutable(list, 0);
+  var bar = inscrutable(list, 1);
+
+  Expect.equals(r'Foo a b c',   foo.m(a: 'a', b: 'b', c: 'c'));
+  Expect.equals(r'Bar z a$b c', bar.m('z', a$b: r'a$b', c: 'c'));
+
+  Expect.throws(() => foo.m('z', a$b: r'a$b', c: 'c'), 
+                (e) => e is NoSuchMethodError);
+  Expect.throws(() => bar.m(a: 'a', b: 'b', c: 'c'),
+                (e) => e is NoSuchMethodError);
+}