Enable WebNavigationApiTest.ServerRedirect test.

This test was flaky due to a race condition in navigation code, which
has now been fixed. Let's try to enable it and see if the fix has helped
deflake this test.

Bug: 660288
Change-Id: I2d8377e42172d30b3af19f23c632d09c3e99f5f3
Reviewed-on: https://chromium-review.googlesource.com/1097555Reviewed-by: Łukasz Anforowicz <lukasza@chromium.org>
Commit-Queue: Nasko Oskov <nasko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#566510}

chrome/browser/extensions/api/web_navigation/web_navigation_apitest.cc

@@ -227,8 +227,7 @@ IN_PROC_BROWSER_TEST_F(WebNavigationApiTest, ClientRedirect) {
       << message_;
 }
 
-// http://crbug.com/660288
-IN_PROC_BROWSER_TEST_F(WebNavigationApiTest, DISABLED_ServerRedirect) {
+IN_PROC_BROWSER_TEST_F(WebNavigationApiTest, ServerRedirect) {
   ASSERT_TRUE(StartEmbeddedTestServer());
   ASSERT_TRUE(RunExtensionTest("webnavigation/serverRedirect"))
       << message_;