Change assert implementation to not depend on a top-level function called 'assert'.

lib/compiler/implementation/lib/js_helper.dart

Index: lib/compiler/implementation/lib/js_helper.dart
diff --git a/lib/compiler/implementation/lib/js_helper.dart b/lib/compiler/implementation/lib/js_helper.dart
index afb3acb83be8268496931bacc242db080cb1f5d7..f13756133eb22a44766b6be9929c6f063f20263e 100644
--- a/lib/compiler/implementation/lib/js_helper.dart
+++ b/lib/compiler/implementation/lib/js_helper.dart
@@ -811,7 +811,7 @@ unwrapException(ex) {
         // Examples:
         //  x.foo is not a function
         //  'undefined' is not a function (evaluating 'x.foo(1,2,3)')
-        // Object doesn't support property or method 'foo' which sets the error 
+        // Object doesn't support property or method 'foo' which sets the error
         // code 438 in IE.
         // TODO(kasperl): Compute the right name if possible.
         return new NoSuchMethodException('', '<unknown>', []);