Fixed type error in browser_controller: DebugLogger.error() takes a string

dart/tools/testing/dart/browser_controller.dart

Index: dart/tools/testing/dart/browser_controller.dart
diff --git a/dart/tools/testing/dart/browser_controller.dart b/dart/tools/testing/dart/browser_controller.dart
index 07afc5a7b1494eaf5c5ad875433ddb329bad4dae..a9992d97e00ea106c4f5fc0b5e48fbd36af7eb3e 100644
--- a/dart/tools/testing/dart/browser_controller.dart
+++ b/dart/tools/testing/dart/browser_controller.dart
@@ -944,7 +944,7 @@ class BrowserTestingServer {
       request.response.close();
       testDoneCallBack(browserId, back, testId);
       // TODO(ricow): We should do something smart if we get an error here.
-    }, onError: (error) { DebugLogger.error(error); });
+    }, onError: (error) { DebugLogger.error("$error"); });
   }
 
   void handleStarted(HttpRequest request, String browserId, var testId) {
@@ -958,7 +958,7 @@ class BrowserTestingServer {
       String back = buffer.toString();
       request.response.close();
       testStartedCallBack(browserId, back, testId);
-    }, onError: (error) { DebugLogger.error(error); });
+    }, onError: (error) { DebugLogger.error("$error"); });
   }
 
   String getNextTest(String browserId) {