Merged r12435 (#15741).
Fixed multiple scrollbars in project tree (#15741).
Merged r12419.
Merged r12420 (#15684).
Merged r12415 (#15677).
Merged r12414 (#15623).
Merged r12349 (#15523).
Merged r12309 (#15398).
make WatchersHelperTest passes when config.threadsafe! is enabled (#12097)
make IssuesHelperTest passes when config.threadsafe! is enabled (#12097)