Generate custom manifests when letting gradle process resources.

Gradle uses package id from manifest when generating R.class. So, we
need to generate a custom manifest if we let gradle process resources.

BUG=682846, webrtc:6328

Review-Url: https://codereview.chromium.org/2691353005
Cr-Commit-Position: refs/heads/master@{#451029}
2 files changed