We use GcmNetworkManager to schedule jobs only for Android L and below:
https://cs.chromium.org/chromium/src/components/background_task_scheduler/android/java/src/org/chromium/components/background_task_scheduler/BackgroundTaskSchedulerFactory.java

However, the class still gets included in monochrome.apk:
https://storage.googleapis.com/chrome-supersize/viewer.html?load_url=milestones%2Farm%2FMonochrome.apk%2Freport_72.0.3626.7.ndjson&method_count=on&include=GcmNetwo&exclude=assets%2Funwind_cfi

We should figure out why and make it not included.