The test has been flaky on the Linux ChromeOS Debug bot. Example log failure:

[ RUN      ] PrerenderBrowserTest.PrerenderCancelSubresourceUnsupportedScheme
[1986:1986:0109/034316.906357:WARNING:chrome_browser_main_chromeos.cc(663)] Running as stub user with profile dir: test-user
[1986:2004:0109/034317.321121:ERROR:logging_chrome.cc(210)] Unable to create symlink /b/s/w/itWCs67B/.org.chromium.Chromium.NhO1Ho/d9UhtpI/test-user/chrome_debug.log pointing at /b/s/w/itWCs67B/.org.chromium.Chromium.NhO1Ho/d9UhtpI/test-user/chrome_debug_20180109-034317: No such file or directory (2)
[1986:2011:0109/034317.850639:WARNING:child_process_launcher_helper_posix.cc(118)] Ignoring invalid file v8_context_snapshot.bin
[2018:2018:0109/034318.080093:WARNING:gpu_info.cc(104)] No active GPU found, returning primary GPU.
[1986:1986:0109/034318.084539:ERROR:wallpaper_controller.cc(1202)] User is ephemeral or guest! Fallback to default wallpaper.
[1986:2005:0109/034318.647027:WARNING:simple_synchronous_entry.cc(1174)] Could not open platform files for entry.
[1986:2013:0109/034318.763723:ERROR:test_database_manager.cc(64)] Not implemented reached in virtual bool safe_browsing::TestSafeBrowsingDatabaseManager::CheckResourceUrl(const GURL &, safe_browsing::SafeBrowsingDatabaseManager::Client *)
[1986:2011:0109/034318.789391:WARNING:child_process_launcher_helper_posix.cc(118)] Ignoring invalid file v8_context_snapshot.bin
[1986:2055:0109/034318.900164:WARNING:embedded_test_server.cc(228)] Request not handled. Returning 404: /favicon.ico
../../chrome/browser/prerender/prerender_browsertest.cc:1050: Failure
Expected equality of these values:
  expected_number_of_loads
    Which is: 0
  prerenders[0]->number_of_loads()
    Which is: 1
../../chrome/browser/prerender/prerender_browsertest.cc:1052: Failure
Expected equality of these values:
  expected_number_of_loads
    Which is: 0
  GetPrerenderLoadEventCountForLinkNumber(0)
    Which is: 1
[1986:1986:0109/034319.460249:INFO:chrome_cryptauth_service.cc(241)] Refresh token not yet available; waiting before starting CryptAuth managers.
[1986:1986:0109/034319.642172:WARNING:url_request_context_getter.cc(43)] URLRequestContextGetter leaking due to no owning thread.
[1986:1986:0109/034319.642230:WARNING:url_request_context_getter.cc(43)] URLRequestContextGetter leaking due to no owning thread.
[  FAILED  ] PrerenderBrowserTest.PrerenderCancelSubresourceUnsupportedScheme, where TypeParam =  and GetParam() =  (3987 ms)