Add unit test to check for broker FD leak

sandbox/linux/tests/unit_tests.cc

Index: sandbox/linux/tests/unit_tests.cc
diff --git a/sandbox/linux/tests/unit_tests.cc b/sandbox/linux/tests/unit_tests.cc
index 2e714aa7412f7b976e62d053f4b51fcd08970dc4..eeb5616fc7817d1724046e72ca980211d0ae5610 100644
--- a/sandbox/linux/tests/unit_tests.cc
+++ b/sandbox/linux/tests/unit_tests.cc
@@ -208,6 +208,17 @@ void UnitTests::DeathSuccess(int status, const std::string& msg, const void*) {
   EXPECT_FALSE(subprocess_exited_but_printed_messages) << details;
 }
 
+void UnitTests::DeathSuccessAllowNoise(int status,
+                                       const std::string& msg,
+                                       const void*) {
+  std::string details(TestFailedMessage(msg));
+
+  bool subprocess_terminated_normally = WIFEXITED(status);
+  ASSERT_TRUE(subprocess_terminated_normally) << details;
+  int subprocess_exit_status = WEXITSTATUS(status);
+  ASSERT_EQ(kExpectedValue, subprocess_exit_status) << details;
+}
+
 void UnitTests::DeathMessage(int status,
                              const std::string& msg,
                              const void* aux) {