Merge cherrypicks of ['android-review.googlesource.com/3028111'] into sparse-12192237-L48700030005686605.
SPARSE_CHANGE: I7c4a1f291bb426ad599e1dc937e6ecd3889b5820
Change-Id: Ia57ae5d45ff59cb31bac1abf985a5e9e466be096
PLATFORM_BASE_OS is used to set value for
ro.build.version.base_os which is used to qualify
a device build as SMR (Security Maintenance Release)
during APFE (Android Partner Approval) to optimize the test span.
See ag/26859560 on how we plan to use this variable.
Add PRODUCT_BASE_OS that can be used to override
PLATFORM_BASE_OS value before making it read_only.
Plan is to set the value for PRODUCT_BASE_OS using build flags.
This way, it can be easily set per device when making on-demand
SMR releases. In future, move it to be set via soong variable
during build process once build system side is ready.
Test: None
Bug: 155105803
(cherry picked from https://android-review.googlesource.com/q/commit:c4baa3aa7240e1b0cb013f853669aa419e55ee1e)
Merged-In: I7c4a1f291bb426ad599e1dc937e6ecd3889b5820
Change-Id: I7c4a1f291bb426ad599e1dc937e6ecd3889b5820