Merge branch 'stable-3.0' into stable-3.1 * stable-3.0: Http: fix generation of the custom readonly message Upgrade bazlets to latest stable-2.16 to build with 2.16.18 API Bump Bazel version to 3.1.0 Change-Id: Ie36732f7dab5a111b89b661eeed1f8bc94bdc46e