Ensure tests have an active task runner

chrome/browser/process_singleton_posix_unittest.cc

 // Copyright 2014 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/process_singleton.h"
 
 #include <fcntl.h>
 #include <signal.h>
 #include <sys/types.h>
 #include <sys/un.h>
@@ skipping 234 matching lines @@
 
   void DestructProcessSingleton() {
     ASSERT_TRUE(process_singleton_on_thread_);
     delete process_singleton_on_thread_;
   }
 
   void KillCallback(int pid) {
     kill_callbacks_++;
   }
 
+  base::MessageLoop message_loop_;
   content::TestBrowserThread io_thread_;
   base::ScopedTempDir temp_dir_;
   base::WaitableEvent wait_event_;
   base::WaitableEvent signal_event_;
 
   scoped_ptr<base::Thread> worker_thread_;
   TestableProcessSingleton* process_singleton_on_thread_;
 };
 
 }  // namespace
@@ skipping 156 matching lines @@
 // Test that if there is an existing lock file, and it's not locked, we replace
 // it.
 TEST_F(ProcessSingletonPosixTest, CreateReplacesOldMacLock) {
   scoped_ptr<TestableProcessSingleton> process_singleton(
       CreateProcessSingleton());
   EXPECT_EQ(0, base::WriteFile(lock_path_, "", 0));
   EXPECT_TRUE(process_singleton->Create());
   VerifyFiles();
 }
 #endif  // defined(OS_MACOSX)