Added support for logging the output of failed flaky tests.

tools/test.dart

Index: tools/test.dart
diff --git a/tools/test.dart b/tools/test.dart
index 2e4990d2a7cfcbe4f18248b6d9d157ad180c7eed..2adc157c717a2f08609d0118a9e3963c17c6c2c9 100755
--- a/tools/test.dart
+++ b/tools/test.dart
@@ -81,6 +81,14 @@ main() {
   var verbose = firstConf['verbose'];
   var printTiming = firstConf['time'];
   var listTests = firstConf['list'];
+  var appendFlakyLog = firstConf['append_flaky_log'];
+  
+  if (!appendFlakyLog)  {
+    var file = new File(FAILED_FLAKY_TESTS_LOGFILE);
+    if (file.existsSync()) {
+      file.deleteSync();
+    }
+  }
 
   // Print the configurations being run by this execution of
   // test.dart. However, don't do it if the silent progress indicator