[Mac] Fix a leak in CookiesWindowControllerTest by giving BrowserTestHelper a fake IO thread.

chrome/browser/cocoa/cookies_window_controller_unittest.mm

Index: chrome/browser/cocoa/cookies_window_controller_unittest.mm
diff --git a/chrome/browser/cocoa/cookies_window_controller_unittest.mm b/chrome/browser/cocoa/cookies_window_controller_unittest.mm
index ea07ff102339c0f77d939b3667515dd5ae75c948..b02031f75e782fe9d0d566706630cd1e706c8bd6 100644
--- a/chrome/browser/cocoa/cookies_window_controller_unittest.mm
+++ b/chrome/browser/cocoa/cookies_window_controller_unittest.mm
@@ -51,8 +51,6 @@ namespace {
 
 class CookiesWindowControllerTest : public CocoaTest {
  public:
-  CookiesWindowControllerTest()
-      : io_thread_(ChromeThread::IO, MessageLoop::current()) {}
 
   virtual void SetUp() {
     CocoaTest::SetUp();
@@ -84,8 +82,6 @@ class CookiesWindowControllerTest : public CocoaTest {
 
  protected:
   BrowserTestHelper browser_helper_;
-  // Need an IO thread to not leak from TestingProfile::CreateRequestContext().
-  ChromeThread io_thread_;
   scoped_nsobject<CookiesWindowController> controller_;
   MockBrowsingDataDatabaseHelper* database_helper_;
   MockBrowsingDataLocalStorageHelper* local_storage_helper_;