[Extensions] Move [Chrome]ExtensionTestNotificationObserver into extensions::

chrome/browser/chromeos/first_run/drive_first_run_browsertest.cc

Index: chrome/browser/chromeos/first_run/drive_first_run_browsertest.cc
diff --git a/chrome/browser/chromeos/first_run/drive_first_run_browsertest.cc b/chrome/browser/chromeos/first_run/drive_first_run_browsertest.cc
index 32cb747db1a335aa214017de921a237cda4e3c08..2fa07a877d151e135f45f4b84d60b33ced3116ab 100644
--- a/chrome/browser/chromeos/first_run/drive_first_run_browsertest.cc
+++ b/chrome/browser/chromeos/first_run/drive_first_run_browsertest.cc
@@ -129,7 +129,7 @@ void DriveFirstRunTest::InstallApp() {
       extensions::CrxInstaller::CreateSilent(extension_service);
 
   installer->InstallCrx(test_data_dir_.AppendASCII(kTestAppCrxName));
-  ChromeExtensionTestNotificationObserver observer(browser());
+  extensions::ChromeExtensionTestNotificationObserver observer(browser());
   observer.WaitForExtensionLoad();
 
   ASSERT_TRUE(extension_service->GetExtensionById(kTestAppId, false));