Add unittest that sandbox::PolicyBase outlives child process.

sandbox/win/tests/common/controller.cc

Index: sandbox/win/tests/common/controller.cc
diff --git a/sandbox/win/tests/common/controller.cc b/sandbox/win/tests/common/controller.cc
index 9f57137c0e7d31844d75addb1590bd7080f6c476..6e45e0ef6c5ac78a41797133f5a58580b5fbb03c 100644
--- a/sandbox/win/tests/common/controller.cc
+++ b/sandbox/win/tests/common/controller.cc
@@ -242,6 +242,10 @@ int TestRunner::InternalRunTest(const wchar_t* command) {
     result = broker_->SpawnTarget(prog_name, arguments.c_str(), policy_,
                                   &warning_result, &last_error, &target);
   }
+  if (release_policy_in_run_) {
+    policy_->Release();
+    policy_ = nullptr;
+  }
 
   if (SBOX_ALL_OK != result)
     return SBOX_TEST_FAILED_TO_RUN_TEST;