Add suppression to test.dart for flaky content_shell crashes

tools/testing/dart/test_progress.dart

Index: tools/testing/dart/test_progress.dart
diff --git a/tools/testing/dart/test_progress.dart b/tools/testing/dart/test_progress.dart
index 3fdfbf3fa734a438dbf45bd27b96aa0c6ec35b84..b93294b389b0a3348edc9a2625fb281e195d8547 100644
--- a/tools/testing/dart/test_progress.dart
+++ b/tools/testing/dart/test_progress.dart
@@ -174,6 +174,31 @@ class ExitCodeSetter extends EventListener {
   }
 }
 
+class IgnoredTestMonitor extends EventListener {
+  static final int maxIgnored = 5;
+
+  int countIgnored = 0;
+
+  void done(TestCase test) {
+    if (test.lastCommandOutput.result(test) == Expectation.IGNORE) {
+      countIgnored++;
+      if (countIgnored > maxIgnored) {
+        print("/nMore than $maxIgnored tests were ignored due to flakes in");
+        print("the test infrastructure. Notify whesse@google.com.");
+        print("Output of the last ignored test was:");
+        print(_buildFailureOutput(test));
+        exit(1);
+      }
+    }
+  }
+
+  void allDone() {
+    if (countIgnored > 0) {
+      print("Ignored $countIgnored tests due to flaky infrastructure");
+    }
+  }
+}
+
 class FlakyLogWriter extends EventListener {
   void done(TestCase test) {
     if (test.isFlaky && test.result != Expectation.PASS) {