update_engine: Update libchrome APIS to r456626.

The new libchrome has been ported from Chromium and some APIs
have changed. Make necessary changes at call sites.

BUG=chromium:724678
CQ-DEPEND=CL:480928
Test: Build.

Change-Id: I4dbaea4a2a19031375a8bf2415645a4f226dab57
diff --git a/update_manager/update_manager_unittest.cc b/update_manager/update_manager_unittest.cc
index 03f1610..c2766ea 100644
--- a/update_manager/update_manager_unittest.cc
+++ b/update_manager/update_manager_unittest.cc
@@ -67,7 +67,9 @@
   now_exp.minute = 5;
   now_exp.second = 33;
   now_exp.millisecond = 675;
-  return Time::FromLocalExploded(now_exp);
+  Time time;
+  ignore_result(Time::FromLocalExploded(now_exp, &time));
+  return time;
 }
 
 }  // namespace