Add sanity checking to declaring class visiting

When we have an unmarked declaring class in the image, it will
SIGSEGV due to the bitmap being read-only. Print some useful
info to try and debug this.

This probably hurts performance a bit, TODO disable when the bug is
fixed.

Bug: 27493510

(cherry picked from commit b33b1dc78d178060ff0f4327d448fd3a89df51de)

Change-Id: I0c25afd5a6101a71fa1494e12dc019ba64bf43be
diff --git a/runtime/gc/space/image_space.h b/runtime/gc/space/image_space.h
index f2f4163..c9741d0 100644
--- a/runtime/gc/space/image_space.h
+++ b/runtime/gc/space/image_space.h
@@ -149,6 +149,8 @@
     return GetImageHeader().GetOatFileEnd();
   }
 
+  void DumpSections(std::ostream& os) const;
+
  protected:
   // Tries to initialize an ImageSpace from the given image path, returning null on error.
   //