ART: Move DexFile vector to Java array

To avoid having native vectors only referenced by Java objects,
which look like leaks to Valgrind, use a Java array to store
references to native DexFile objects.

Change-Id: If3c2b31b9d0914ed1965cfd5e3fdb94ea41b1477
diff --git a/runtime/native/dalvik_system_DexFile.h b/runtime/native/dalvik_system_DexFile.h
index 487df05..7585ab9 100644
--- a/runtime/native/dalvik_system_DexFile.h
+++ b/runtime/native/dalvik_system_DexFile.h
@@ -21,6 +21,8 @@
 
 namespace art {
 
+class DexFile;
+
 void register_dalvik_system_DexFile(JNIEnv* env);
 
 }  // namespace art