Revert "Remove an old hack from test_main_lib.cc."

This reverts commit 5114a927aaa373f98120b2f41469be6679cac539.

Reason for revert: Breaks downstream.

Original change's description:
> Remove an old hack from test_main_lib.cc.
> 
> Bug: webrtc:9792
> Change-Id: I0464f08bcc023dcbcaec595fc9ebb5bfe0736f68
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/155441
> Reviewed-by: Niels Moller <nisse@webrtc.org>
> Commit-Queue: Patrik Höglund <phoglund@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#29376}

TBR=phoglund@webrtc.org,nisse@webrtc.org

Change-Id: I40f563fa3fc6ab289d72a1e7d9e4fb3fdc2669ae
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:9792
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/155584
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Commit-Queue: Patrik Höglund <phoglund@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29380}
diff --git a/test/test_main_lib.cc b/test/test_main_lib.cc
index 59352ca..bb41e65 100644
--- a/test/test_main_lib.cc
+++ b/test/test_main_lib.cc
@@ -124,6 +124,13 @@
       rtc::tracing::StartInternalCapture(trace_event_path.c_str());
     }
 
+    // TODO(bugs.webrtc.org/9792): we need to reference something from
+    // fileutils.h so that our downstream hack where we replace fileutils.cc
+    // works. Otherwise the downstream flag implementation will take over and
+    // botch the flag introduced by the hack. Remove this awful thing once the
+    // downstream implementation has been eliminated.
+    (void)webrtc::test::JoinFilename("horrible", "hack");
+
     // InitFieldTrialsFromString stores the char*, so the char array must
     // outlive the application.
     field_trials_ = absl::GetFlag(FLAGS_force_fieldtrials);