Bug 868521 - Add more of a delay between launching a new app and creating a new preallocated process. r=dhylands
Bug 870181 - Part 1: Add an additional LowCPUPriority argument to hal::SetProcessPriority. r=bent

This patch also makes it an error to call hal::SetProcessPriority from a child process.
Bug 870181 - Part 2: Lower CPU priority for non-high priority processes when there's an incoming call. r=bent
Bug 870181 - Part 3: Test that we downgrade processes' CPU priorities when appropriate. r=bent