Add oatdump support for app images

Example usage on host:
oatdumpd --app-oat=art/plus32.odex --app-image=art/plus32.art
--image=art/oats/system@framework@boot.art --instruction-set=arm

TODO: Add to oatdump test.

Bug: 27408512
Bug: 22858531

(cherry picked from commit bcb6a72569a1401b36a3ad3b6aa4d13e29966cf0)

Change-Id: I9d1aa7eaa16795e5fbabc6974d245849e16b1d03
diff --git a/runtime/class_linker.h b/runtime/class_linker.h
index 492a228..36ed820 100644
--- a/runtime/class_linker.h
+++ b/runtime/class_linker.h
@@ -149,6 +149,12 @@
       REQUIRES(!dex_lock_)
       SHARED_REQUIRES(Locks::mutator_lock_);
 
+  bool OpenImageDexFiles(gc::space::ImageSpace* space,
+                         std::vector<std::unique_ptr<const DexFile>>* out_dex_files,
+                         std::string* error_msg)
+      REQUIRES(!dex_lock_)
+      SHARED_REQUIRES(Locks::mutator_lock_);
+
   // Finds a class by its descriptor, loading it if necessary.
   // If class_loader is null, searches boot_class_path_.
   mirror::Class* FindClass(Thread* self,