update_engine: fix english

Fix the english for accuracy regarding DLC.

BUG=chromium:897882
TEST=None

Change-Id: I72ab9ecb7903bb5fb35597222cd7c8b1f4244cfc
Reviewed-on: https://chromium-review.googlesource.com/1351359
Commit-Ready: Xiaochu Liu <xiaochu@chromium.org>
Tested-by: Xiaochu Liu <xiaochu@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
diff --git a/mock_update_attempter.h b/mock_update_attempter.h
index eaa0785..c5fcec8 100644
--- a/mock_update_attempter.h
+++ b/mock_update_attempter.h
@@ -53,7 +53,7 @@
                     UpdateAttemptFlags flags));
 
   MOCK_METHOD2(CheckForInstall,
-               bool(const std::vector<std::string>& dlc_ids,
+               bool(const std::vector<std::string>& dlc_module_ids,
                     const std::string& omaha_url));
 
   MOCK_METHOD0(RefreshDevicePolicy, void(void));