ART: Only allow the zygote to create the global boot image

Do not allow arbitrary processes, even when root, to write the
boot image in /data/dalvik-cache.

Bug: 17478752, 17510489, 17439961
Change-Id: Iba2b74be6d0752f4221f4ff5ee295b45a34cb2e1
(cherry picked from commit 33c36d4f22ab6a5e61eb47b654deaf647c34e49c)
diff --git a/runtime/gc/space/image_space.h b/runtime/gc/space/image_space.h
index 28ebca6..2586ece 100644
--- a/runtime/gc/space/image_space.h
+++ b/runtime/gc/space/image_space.h
@@ -110,7 +110,8 @@
                                 bool* has_system,
                                 std::string* data_location,
                                 bool* dalvik_cache_exists,
-                                bool* has_data);
+                                bool* has_data,
+                                bool *is_global_cache);
 
  private:
   // Tries to initialize an ImageSpace from the given image path,