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

tests/language/private_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.
+
+library a;
+
+import 'private_clash_lib.dart' as lib;
+import 'package:expect/expect.dart';
+
+class A extends lib.B {
+  var _b$_c$ = 100; // With library prefix: _a$_b$_c$
+
+  getValueB() {
+    try {} catch(e) {} // no inline
+    return this._b$_c$;
+  }
+}
+
+main() {
+  A a = new A();
+  Expect.equals(110, a.getValueA() + a.getValueB());
+}