Register proxy natives declared in @MainDex properly

Previously the @MainDex annotation would not be processed by
the jni_generator for proxy natives. So method registrations
that should be in main dex were incorrectly registered.

This CL processes @MainDex annotations for proxy natives
and properly splits up their declaration in generated
registration headers.

Bug: 898261
Change-Id: Iad9d3b3121085ef1427b958dcefc1acfb255312c
Reviewed-on: https://chromium-review.googlesource.com/c/1303394
Commit-Queue: Aiden Benner <abenner@google.com>
Reviewed-by: agrieve <agrieve@chromium.org>
Reviewed-by: Eric Stevenson <estevenson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604014}
6 files changed