Fix PrerenderBrowserTest.AutosigninInPrerenderer flakiness.

chrome/browser/prerender/prerender_browsertest.cc

Index: chrome/browser/prerender/prerender_browsertest.cc
diff --git a/chrome/browser/prerender/prerender_browsertest.cc b/chrome/browser/prerender/prerender_browsertest.cc
index b6f790c852164df2a639e9748964cc31608f7420..b7787f9d950507547ed438ac05cb7e88f656d318 100644
--- a/chrome/browser/prerender/prerender_browsertest.cc
+++ b/chrome/browser/prerender/prerender_browsertest.cc
@@ -3217,9 +3217,7 @@ IN_PROC_BROWSER_TEST_F(PrerenderBrowserTest, HttpPost) {
 
 // Prerenders a page that tries to automatically sign user in via the Credential
 // Manager API. The page should be killed.
-//
-// Disabled. See http://crbug.com/660278
-IN_PROC_BROWSER_TEST_F(PrerenderBrowserTest, DISABLED_AutosigninInPrerenderer) {
+IN_PROC_BROWSER_TEST_F(PrerenderBrowserTest, AutosigninInPrerenderer) {
   // Set up a credential in the password store.
   PasswordStoreFactory::GetInstance()->SetTestingFactory(
       current_browser()->profile(),
@@ -3251,6 +3249,8 @@ IN_PROC_BROWSER_TEST_F(PrerenderBrowserTest, DISABLED_AutosigninInPrerenderer) {
       BrowserThread::IO, FROM_HERE,
       base::Bind(&CreateCountingInterceptorOnIO,
                  done_url, empty_file, done_counter.AsWeakPtr()));
+  // Loading may finish or be interrupted. The final result is important only.
+  DisableLoadEventCheck();

[pasko, 2016/10/28 11:39:54]

It seems that FINAL_STATUS_APP_TERMINATING can happen as well if:
1. load did not happen
2. the test gets to the end sooner than the auto-signin manage to kill the
webcontents

Wouldn't the problem be solved by 'just' providing expected_number_of_loads=1
toPrerenderTestURL()?

AFAICT the autosignin.html pokes to Credential Manager API after the onload
event. Is that signal strictly ordered against the onload IPC?

Then, if my assumptions about ordering are true, to eliminate the possibility of
FINAL_STATUS_APP_TERMINATING (and make the done_counter check more
deterministic) we would run TestPrerender::WaitForStop() before
EXPECT.*done_counter.

   PrerenderTestURL("/password/autosignin.html",
                    FINAL_STATUS_CREDENTIAL_MANAGER_API, 0);
   EXPECT_EQ(0, done_counter.count());