Reenable CleanerSandboxInterface.DeleteService_HandleHeld for debugging

We currently do not have sufficient tools to repro failure on bot without
enable the test.

Bug: 956016
Change-Id: I89a97d78310fbae96016909196e56cd33ead9230
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1914295Reviewed-by: Joe Mason <joenotcharles@chromium.org>
Commit-Queue: Sven Zheng <svenzheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715017}

chrome/chrome_cleaner/engines/broker/cleaner_sandbox_interface_unittest.cc

@@ -801,8 +801,11 @@ TEST(CleanerSandboxInterface, DISABLED_DeleteService_Running) {
   EXPECT_FALSE(chrome_cleaner::DoesServiceExist(service_handle.service_name()));
 }
 
-// Disabled: https://crbug.com/956016
-TEST(CleanerSandboxInterface, DISABLED_DeleteService_HandleHeld) {
+// Temporarily enable for debugging flakiness.
+// Trooper can ignore this test. Further info refer to
+// https://crbug.com/956016
+// Updated by svenzheng@chromium.org, 2019-11-13.
+TEST(CleanerSandboxInterface, DeleteService_HandleHeld) {
   ASSERT_TRUE(chrome_cleaner::EnsureNoTestServicesRunning());
 
   chrome_cleaner::TestScopedServiceHandle service_handle;