Debug information for failing navigations

Unfortunately, the previous CL
(https://chromium-review.googlesource.com/1218902) lacked an important
negation.

TBR=sky@chromium.org

Bug: 882545
Change-Id: I730dbab7c05b0d67c11be67437b462ac51afd7b3
Reviewed-on: https://chromium-review.googlesource.com/1219750Reviewed-by: Dominic Battré <battre@chromium.org>
Commit-Queue: Dominic Battré <battre@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590325}

content/public/test/content_browser_test_utils.cc

@@ -53,7 +53,7 @@ void NavigateToURLBlockUntilNavigationsComplete(Shell* window,
   same_tab_observer.Wait();
   // TODO(crbug.com/882545) Delete this if statement once the problem has been
   // identified.
-  if (same_tab_observer.last_navigation_succeeded()) {
+  if (!same_tab_observer.last_navigation_succeeded()) {
     DLOG(WARNING) << "Last navigation to " << url << " failed with net error "
                   << same_tab_observer.last_net_error_code();
   }