chromeos: Use base::MessageLoop.

BUG=236029
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Review URL: https://codereview.chromium.org/15774005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@202997 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/chromeos/disks/disk_mount_manager_unittest.cc b/chromeos/disks/disk_mount_manager_unittest.cc
index aa1b1f4..3161818 100644
--- a/chromeos/disks/disk_mount_manager_unittest.cc
+++ b/chromeos/disks/disk_mount_manager_unittest.cc
@@ -200,7 +200,7 @@
  protected:
   chromeos::FakeCrosDisksClient* fake_cros_disks_client_;
   MockDiskMountManagerObserver observer_;
-  MessageLoopForUI message_loop_;
+  base::MessageLoopForUI message_loop_;
 };
 
 // Tests that the observer gets notified on attempt to format non existent mount