Add HeapTest and make GC work enough to pass it

Change-Id: If06eaef2921b64b3226bfd347acaec60ec993e67
diff --git a/src/image_writer.h b/src/image_writer.h
index 4299373..80012bc 100644
--- a/src/image_writer.h
+++ b/src/image_writer.h
@@ -11,6 +11,7 @@
 #include "mem_map.h"
 #include "object.h"
 #include "os.h"
+#include "space.h"
 
 namespace art {