gn2bp: Add java files to the srcs of cronet_jni_registration

jni_registration_generator.py takes the java file paths from the sources
files. But the path in the original file does not work in genrule.
This CL add the required java files to the srcs of
cronet_jni_registration.
Upcoming CL generates source file from the srcs and make
jni_registration_generator.py use the generated source file

Test: ./update_results.sh
Change-Id: Idf74664713b7af614b132bdd456a8a9e2e8876de