Only generate assert in checked mode.

lib/compiler/implementation/lib/mock.dart

Index: lib/compiler/implementation/lib/mock.dart
===================================================================
--- lib/compiler/implementation/lib/mock.dart	(revision 8394)
+++ lib/compiler/implementation/lib/mock.dart	(working copy)
@@ -28,7 +28,9 @@
 // TODO(ahe): VM specfic exception?
 class StaticResolutionException implements Exception {}
 
-void assert(condition) {}
+void assert(condition) {

[kasperl, 2012/06/08 05:34:05]

I think this needs a bit more work. Something like this:

   void assert(object) {
     bool condition = (object is Function) 
         ? object() 
         : object;
     // TODO(kasperl): What should we do if condition is
     // null. Doesn't seem to be handled by the spec.
     if (!condition) throw new AssertionError();
   }

Excerpt from the spec
---------------------
The conditional expression e is evaluated to an object o. If the class of o is
a subtype of Function then let r be the result of invoking o with no arguments.
Otherwise, let r be o. It is a dynamic type error if o is not of type bool or
of type Function, or if r is not of type bool. If r is false, we say that the
assertion failed. If r is true, we say that the assertion succeeded. If the
assertion
succeeded, execution of the assert statement is complete. If the assertion
failed,
an AssertionError is thrown.

[ngeoffray, 2012/06/08 09:40:58]

Done.

+  if (condition !== true) throw new AssertionError();
+}
 
 // TODO(ahe): Not sure ByteArray belongs in the core library.
 interface Uint8List extends List default _InternalByteArray {