Add unit test to check for broker FD leak

sandbox/linux/tests/unit_tests.h

Index: sandbox/linux/tests/unit_tests.h
diff --git a/sandbox/linux/tests/unit_tests.h b/sandbox/linux/tests/unit_tests.h
index 3f6092e1443e8ad5b76164cea9faaa1f985c6119..0cb682b0615731fcea69f5b201e7639a896e94a8 100644
--- a/sandbox/linux/tests/unit_tests.h
+++ b/sandbox/linux/tests/unit_tests.h
@@ -40,6 +40,8 @@ bool IsRunningOnValgrind();
 //       gtests's ASSERT_XXX() macros instead of SANDBOX_ASSERT(). See
 //       unit_tests.cc for examples.
 #define DEATH_SUCCESS() sandbox::UnitTests::DeathSuccess, NULL
+#define DEATH_SUCCESS_ALLOW_NOISE() \
+  sandbox::UnitTests::DeathSuccessAllowNoise, NULL
 #define DEATH_MESSAGE(msg)          \
   sandbox::UnitTests::DeathMessage, \
       static_cast<const void*>(static_cast<const char*>(msg))
@@ -68,6 +70,11 @@ bool IsRunningOnValgrind();
 #define SANDBOX_TEST(test_case_name, test_name) \
   SANDBOX_DEATH_TEST(test_case_name, test_name, DEATH_SUCCESS())
 
+// SANDBOX_TEST_ALLOW_NOISE is just like SANDBOX_TEST, except it does not
+// consider log error messages printed by the test to be test failures.
+#define SANDBOX_TEST_ALLOW_NOISE(test_case_name, test_name) \
+  SANDBOX_DEATH_TEST(test_case_name, test_name, DEATH_SUCCESS_ALLOW_NOISE())
+
 // Simple assertion macro that is compatible with running inside of a death
 // test. We unfortunately cannot use any of the GTest macros.
 #define SANDBOX_STR(x) #x
@@ -109,6 +116,12 @@ class UnitTests {
   // of this DeathCheck is unused (and thus unnamed)
   static void DeathSuccess(int status, const std::string& msg, const void*);
 
+  // A DeathCheck method that verifies that the test completed succcessfully
+  // allowing for log error messages.
+  static void DeathSuccessAllowNoise(int status,
+                                     const std::string& msg,
+                                     const void*);
+
   // A DeathCheck method that verifies that the test completed with error
   // code "1" and printed a message containing a particular substring. The
   // "aux" pointer should point to a C-string containing the expected error