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: I01b70da87521d0884ed21acbd7ed3e0ff1e94357
Merged-In: I4dbaea4a2a19031375a8bf2415645a4f226dab57
diff --git a/update_manager/real_time_provider.cc b/update_manager/real_time_provider.cc
index ca3acad..db26816 100644
--- a/update_manager/real_time_provider.cc
+++ b/update_manager/real_time_provider.cc
@@ -43,7 +43,10 @@
     Time::Exploded now_exp;
     clock_->GetWallclockTime().LocalExplode(&now_exp);
     now_exp.hour = now_exp.minute = now_exp.second = now_exp.millisecond = 0;
-    return new Time(Time::FromLocalExploded(now_exp));
+    Time* now = new Time();
+    bool success = Time::FromLocalExploded(now_exp, now);
+    DCHECK(success);
+    return now;
   }
 
  private: