Add a mojo bridge for PersistentPrefStore.

chrome/browser/profiles/profile_browsertest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/profiles/profile.h"
 
 #include <stddef.h>
 
 #include <memory>
 
@@ skipping 659 matching lines @@
   }
 #endif
 
   // This retry loop reduces flakiness due to the fact that this ultimately
   // tests whether or not a code path hits a timed wait.
   bool succeeded = false;
   for (size_t retries = 0; !succeeded && retries < 3; ++retries) {
     // Flush the profile data to disk for all loaded profiles.
     profile->SetExitType(Profile::EXIT_CRASHED);
     profile->GetPrefs()->CommitPendingWrite();
+    FlushTaskRunner(content::BrowserThread::GetTaskRunnerForThread(
+                        content::BrowserThread::IO)
+                        .get());
     FlushTaskRunner(profile->GetIOTaskRunner().get());
 
     // Make sure that the prefs file was written with the expected key/value.
     ASSERT_EQ(GetExitTypePreferenceFromDisk(profile), "Crashed");
 
     // The blocking wait in EndSession has a timeout.
     base::Time start = base::Time::Now();
 
     // This must not return until the profile data has been written to disk.
     // If this test flakes, then logoff on Windows has broken again.
@@ skipping 156 matching lines @@
       base::Bind(&SendReportHttpResponse, embedded_test_server()->base_url()));
   ASSERT_TRUE(hpkp_test_server.Start());
 
   // To send a report, must use a non-numeric host name for the original
   // request.  This must not match the host name of the server that reports are
   // sent to.
   ui_test_utils::NavigateToURL(browser(),
                                hpkp_test_server.GetURL("localhost", "/"));
   wait_for_report_loop.Run();
 }