gn2bp: Set --py-out-dir arg in protoc_wrapper.py

Test: ./update_result.sh
Change-Id: Ifbc186e988111d36b081bd753b3d98e5bec44b64
diff --git a/tools/gn2bp/gen_android_bp b/tools/gn2bp/gen_android_bp
index 0d59c4f..c57011c 100755
--- a/tools/gn2bp/gen_android_bp
+++ b/tools/gn2bp/gen_android_bp
@@ -883,6 +883,8 @@
         # So, for now, adding specific for this target.
         module.srcs.add(target.args[i+1])
         target.args[i + 1] = '$(location %s)' % target.args[i + 1]
+      elif val == "--py-out-dir":
+        target.args[i + 1] = '$(genDir)/' + target.args[i + 1]
 
   script = gn_utils.label_to_path(target.script)
   module.tool_files.add(script)