Handle APKs with only loadable modules.

Update the checks in rules.gni so that _native_libs_file_arg is set in
the same cases that it is used; otherwise APKs that contain a loadable
module but not a "main" shared library fail.

Change-Id: I88e0c169199af9625dcb7750f9bcd0a9b3dca4b7
Reviewed-on: https://chromium-review.googlesource.com/1238781
Reviewed-by: Eric Stevenson <estevenson@chromium.org>
Commit-Queue: Richard Coles <torne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593277}
1 file changed