Disable DriveFsBidirectionalNativeMessaging flag in tests by default

Tests expect this flag to be disabled, so this change ensures that, and
allows the flag to be used in a field trial testing configuration.

Bug: 1067346
Change-Id: I403ad113042de65f4ae7c9e888ce94124f7788f6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2610410Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Commit-Queue: Austin Tankiang <austinct@chromium.org>
Cr-Commit-Position: refs/heads/master@{#840093}

chrome/browser/chromeos/file_manager/file_manager_browsertest_base.cc

@@ -1694,6 +1694,9 @@ void FileManagerBrowserTestBase::SetUpCommandLine(
   if (options.drive_dss_pin) {
     enabled_features.push_back(
         chromeos::features::kDriveFsBidirectionalNativeMessaging);
+  } else {
+    disabled_features.push_back(
+        chromeos::features::kDriveFsBidirectionalNativeMessaging);
   }
 
   if (options.enable_sharesheet) {