Merge branch 'stable-3.2' into stable-3.3
* stable-3.2:
ContentTypeUtil: Add singleton scope
Upgrade bazlets to latest stable-3.1 to build with 3.1.12 API
Upgrade bazlets to latest stable-3.0 to build with 3.0.15 API
Upgrade bazlets to latest stable-2.16 to build with 2.16.26 API
Upgrade bazlets to latest stable-3.2 to build with 3.2.6 API
Upgrade bazlets to latest stable-3.1 to build with 3.1.11 API
Upgrade bazlets to latest stable-2.16 to build with 2.16.23 API
Change-Id: I6f872661664235fa58eee326262f1c9ad9737623