Fix broken assertion.

dart/lib/compiler/implementation/dart2js.dart

Index: dart/lib/compiler/implementation/dart2js.dart
diff --git a/dart/lib/compiler/implementation/dart2js.dart b/dart/lib/compiler/implementation/dart2js.dart
index 0e0f0315fae71073421c17d28721e764a6f4fb80..b1420432df999e742aed59535edea2a16dcff6ee 100644
--- a/dart/lib/compiler/implementation/dart2js.dart
+++ b/dart/lib/compiler/implementation/dart2js.dart
@@ -35,9 +35,9 @@ void parseCommandLine(List<OptionHandler> handlers, List<String> argv) {
     patterns.add(handler.pattern);
   }
   var pattern = new RegExp('^(${Strings.join(patterns, ")|(")})\$');
-  assert(pattern.groupCount() == handlers.length);
   OUTER: for (String argument in argv) {
     Match match = pattern.firstMatch(argument);
+    assert(match.groupCount() == handlers.length);
     for (int i = 0; i < handlers.length; i++) {
       if (match[i + 1] !== null) {
         handlers[i].handle(argument);