Make image test multi image

Required for testing multi image layout in future CLs.

Bug: 28640955

Test: clean-oat-host, test-art-host, device booting

(cherry picked from commit 25adcfb7dc81131add3a0a681ae18bced6f7a0e0)

Change-Id: I14809f56e711b4a87e01056c327eddbbd087f4ee
diff --git a/runtime/gc/space/image_space.h b/runtime/gc/space/image_space.h
index c407259..0ba131b 100644
--- a/runtime/gc/space/image_space.h
+++ b/runtime/gc/space/image_space.h
@@ -125,10 +125,14 @@
 
   // Use the input image filename to adapt the names in the given boot classpath to establish
   // complete locations for secondary images.
-  static void CreateMultiImageLocations(const std::string& input_image_file_name,
+  static void ExtractMultiImageLocations(const std::string& input_image_file_name,
                                         const std::string& boot_classpath,
                                         std::vector<std::string>* image_filenames);
 
+  static std::string GetMultiImageBootClassPath(const std::vector<const char*>& dex_locations,
+                                                const std::vector<const char*>& oat_filenames,
+                                                const std::vector<const char*>& image_filenames);
+
   // Return the end of the image which includes non-heap objects such as ArtMethods and ArtFields.
   uint8_t* GetImageEnd() const {
     return Begin() + GetImageHeader().GetImageSize();