Replace FOR_EACH_OBSERVER in chromeos/ with range-based for

chromeos/disks/mock_disk_mount_manager.cc

Index: chromeos/disks/mock_disk_mount_manager.cc
diff --git a/chromeos/disks/mock_disk_mount_manager.cc b/chromeos/disks/mock_disk_mount_manager.cc
index 07596db6cb20f3619c6fec83083b00dc1e8546f0..99ba785a7094478a932fe0aed5bbc32d5de78b56 100644
--- a/chromeos/disks/mock_disk_mount_manager.cc
+++ b/chromeos/disks/mock_disk_mount_manager.cc
@@ -218,12 +218,14 @@ void MockDiskMountManager::EnsureMountInfoRefreshedInternal(
 void MockDiskMountManager::NotifyDiskChanged(
     DiskEvent event,
     const DiskMountManager::Disk* disk) {
-  FOR_EACH_OBSERVER(Observer, observers_, OnDiskEvent(event, disk));
+  for (auto& observer : observers_)
+    observer.OnDiskEvent(event, disk);
 }
 
 void MockDiskMountManager::NotifyDeviceChanged(DeviceEvent event,
                                                const std::string& path) {
-  FOR_EACH_OBSERVER(Observer, observers_, OnDeviceEvent(event, path));
+  for (auto& observer : observers_)
+    observer.OnDeviceEvent(event, path);
 }
 
 }  // namespace disks