Use unique_ptr to track ownership of dex files.

Bug: 18809837
Change-Id: Ie571eae8fc19ee9207390cff5c7e2a38071b126a
diff --git a/runtime/mirror/dex_cache_test.cc b/runtime/mirror/dex_cache_test.cc
index ef6fc67..53e5534 100644
--- a/runtime/mirror/dex_cache_test.cc
+++ b/runtime/mirror/dex_cache_test.cc
@@ -34,6 +34,7 @@
 TEST_F(DexCacheTest, Open) {
   ScopedObjectAccess soa(Thread::Current());
   StackHandleScope<1> hs(soa.Self());
+  ASSERT_TRUE(java_lang_dex_file_ != NULL);
   Handle<DexCache> dex_cache(
       hs.NewHandle(class_linker_->AllocDexCache(soa.Self(), *java_lang_dex_file_)));
   ASSERT_TRUE(dex_cache.Get() != NULL);