Exit with an error on unexpected command line arguments.

sdk/lib/_internal/pub/lib/src/command/cache.dart

Index: sdk/lib/_internal/pub/lib/src/command/cache.dart
diff --git a/sdk/lib/_internal/pub/lib/src/command/cache.dart b/sdk/lib/_internal/pub/lib/src/command/cache.dart
index ec0d181328407103251b819838d7e84f7a067144..29ad06bd4ed5b9cd87b08f060f340a085929fba7 100644
--- a/sdk/lib/_internal/pub/lib/src/command/cache.dart
+++ b/sdk/lib/_internal/pub/lib/src/command/cache.dart
@@ -18,8 +18,10 @@ class CacheCommand extends PubCommand {
   String get usage => 'pub cache list';
   bool get hidden => true;
   bool get requiresEntrypoint => false;
+  bool get takesArguments => true;
 
   Future onRun() {
+    // TODO(rnystrom): Use subcommand for "list".
     if (commandOptions.rest.length != 1) {
       log.error('The cache command expects one argument.');
       this.printUsage();