[Extensions] Fix flakiness with a Content Settings API test.

This test is flaky for Service Worker-based extensions due to
reloading to remove file access. This CL adds the kEnableFileAccess
flag as a workaround.

Bug: 1127564
Change-Id: I9fe5728639169bdcb8ea8d05f3cb0081675cdd18
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2560608
Commit-Queue: David Bertoni <dbertoni@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Auto-Submit: David Bertoni <dbertoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832027}

chrome/browser/extensions/api/content_settings/content_settings_apitest.cc

@@ -241,7 +241,10 @@ class ExtensionContentSettingsApiLazyTest
 
  protected:
   bool RunLazyTest(const std::string& extension_name) {
-    int browser_test_flags = kFlagNone;
+    // TODO(https://crbug.com/1146173): These tests are being run with
+    // file access to prevent flakiness for the SW version. This should
+    // be reverted to run without file access when this bug is fixed.
+    int browser_test_flags = kFlagEnableFileAccess;
     if (GetParam() == ContextType::kServiceWorker)
       browser_test_flags |= kFlagRunAsServiceWorkerBasedExtension;