Add backend to dumps

Fixes: b/231424162
Change-Id: Ifd4d7676f104a4ca1f160522cb2840aefefba06b
diff --git a/tools/compiledump.py b/tools/compiledump.py
index 691bdeb..52805f9 100755
--- a/tools/compiledump.py
+++ b/tools/compiledump.py
@@ -289,11 +289,8 @@
   return dump.program_jar()
 
 def determine_class_file(args, build_properties):
-  if args.classfile:
-    return args.classfile
-  if 'classfile' in build_properties:
-    return True
-  return None
+  return args.classfile \
+      or build_properties.get('backend', 'dex').lower() == 'cf'
 
 def determine_android_platform_build(args, build_properties):
   if args.android_platform_build: