Start implementing checked mode and tools support for using it.

lib/compiler/implementation/lib/mock.dart

Index: lib/compiler/implementation/lib/mock.dart
===================================================================
--- lib/compiler/implementation/lib/mock.dart	(revision 7269)
+++ lib/compiler/implementation/lib/mock.dart	(working copy)
@@ -7,7 +7,11 @@
 // TODO(ahe): Remove this file.
 
 class AssertionError {}
-class TypeError extends AssertionError {}
+class TypeError extends AssertionError {
+  String msg;

[kasperl, 2012/05/07 10:42:39]

final?

[ngeoffray, 2012/05/07 13:15:42]

Done.

+  TypeError(this.msg);

[kasperl, 2012/05/07 10:42:39]

const?

[ngeoffray, 2012/05/07 13:15:42]

Done.

+  toString() => msg;
+}
 
 class FallThroughError {
   const FallThroughError();