Add additional_jar_files to inputs for java_library targets.

build/config/android/rules.gni

Index: build/config/android/rules.gni
diff --git a/build/config/android/rules.gni b/build/config/android/rules.gni
index facedb5f8404f2ea19fabbaae7f96ac46aef29d7..9894b5a72cd740701138278a9fd0fc9c5a7008d2 100644
--- a/build/config/android/rules.gni
+++ b/build/config/android/rules.gni
@@ -1179,6 +1179,11 @@ if (enable_java_templates) {
   #     dependencies for this target. This will allow depending on an
   #     android_library target, for example.
   #
+  #   additional_jar_files: Use to package additional files into the output jar.
+  #     Pass a list of length-2 lists with format
+  #     [ [ path_to_file, path_to_put_in_jar ] ]
+  #
+  #
   #   data_deps, testonly
   #
   # Example