Bugzilla

Currently we use x86 instrumented builds to generate profile data for arm32 shippable builds, and x86_64 for aarch64.

I see a 3 to 4% improvement in speedometer3 score when doing an aarch64 build using profile data I generated locally from an aarch64 instrumented build compared to an x86_64 one. (By hacking the android_emulator_pgo.py script to run locally and performing the profile generation in an emulator on my M2 macbook).

In terms of performing these builds in CI:
* Recent android arm64 system images cannot be emulated on an x86_64 host. However, we may be able to use an older android version system image. Prior to bug 1718341 we used an arm32 image, but we switched away for a reason.
* Recent x86_64 system images can be run on an x86_64, and are [able to run aarch64 binaries](https://android-developers.googleblog.com/2020/03/run-arm-apps-on-android-emulator.html). However, we need to use the `google_apis` variant, and I'm not sure whether that's okay.
* Perhaps we can run an aarch64 system image on an aarch64 Linux host

Currently we use x86 instrumented builds to generate profile data for arm32 shippable builds, and x86_64 for aarch64.

I see a 3 to 4% improvement in speedometer3 score when doing an aarch64 build using profile data I generated locally from an aarch64 instrumented build compared to an x86_64 one. (By hacking the android_emulator_pgo.py script to run locally and performing the profile generation in an emulator on my M2 macbook).

In terms of performing these builds in CI:
* Recent android arm64 system images cannot be emulated on an x86_64 host. However, we may be able to use an older android version system image. Prior to bug 1718341 we used an arm32 image, but we switched away for a reason.
* Recent x86_64 system images can obviously be run on an x86_64 host, and are [able to run aarch64 binaries](https://android-developers.googleblog.com/2020/03/run-arm-apps-on-android-emulator.html). However, we need to use the `google_apis` variant, and I'm not sure whether that's okay.
* Perhaps we can run an aarch64 system image on an aarch64 Linux host