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

tests/compiler/dart2js/pretty_parameter_test.dart

Index: tests/compiler/dart2js/pretty_parameter_test.dart
diff --git a/tests/compiler/dart2js/pretty_parameter_test.dart b/tests/compiler/dart2js/pretty_parameter_test.dart
index 723683b38122e7a07322c7be83af3b964a1a9f55..34059d5284fc42e7bf77f4bfdbee3661e0c27f7c 100644
--- a/tests/compiler/dart2js/pretty_parameter_test.dart
+++ b/tests/compiler/dart2js/pretty_parameter_test.dart
@@ -79,7 +79,7 @@ main() {
     }),
 
     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) {