Change marking objects in to_space DCHECK to CHECK

Should have no visible performance hit since the check should only
happen for large objects.

Working on pinpointing bug 12897879

Change-Id: I5cacf5275af8367997a595b72d42474a909ff10f
diff --git a/runtime/gc/collector/semi_space.cc b/runtime/gc/collector/semi_space.cc
index 625f869..3fb78b0 100644
--- a/runtime/gc/collector/semi_space.cc
+++ b/runtime/gc/collector/semi_space.cc
@@ -502,7 +502,7 @@
           MarkStackPush(obj);
         }
       } else {
-        DCHECK(!to_space_->HasAddress(obj)) << "Marking object in to_space_";
+        CHECK(!to_space_->HasAddress(obj)) << "Marking object in to_space_";
         if (MarkLargeObject(obj)) {
           MarkStackPush(obj);
         }