Add --image-classes to dex2oat

Change-Id: Ia88f9d302e0f9cd72be2199ee46d212d99864c67
diff --git a/src/dex_file.h b/src/dex_file.h
index 92aa794..a7026d6 100644
--- a/src/dex_file.h
+++ b/src/dex_file.h
@@ -176,7 +176,7 @@
                                         const ClassPath& class_path);
 
   // Opens a collection of .dex files
-  static void OpenDexFiles(std::vector<const char*>& dex_filenames,
+  static void OpenDexFiles(const std::vector<const char*>& dex_filenames,
                            std::vector<const DexFile*>& dex_files,
                            const std::string& strip_location_prefix);