Renderer notifications of memory pressure have been removed in https://codereview.chromium.org/2882513004/ but there's still several MemoryPressureObserver objects created in the renderer/browser processes. These observers are useless because there's no signal being sent to them (the memory pressure monitor object only exist in the browser process).

I think that these observers should be removed and that comment should be added to the appropriate files to specify that the memory pressure signals are only implemented in the browser process. Having these unused observers might create some confusion as people could rely on them and/or waste some time trying to improve them. 

We'll probably need to add some other observers once we have a better memory pressure signal, but we're not there yet.


(Most of the observers are listed in this document: https://docs.google.com/spreadsheets/d/1tAJGcp2T6RFyag4zFNAOnpmuztTrz0WRNES5pBS9GTs/edit?usp=sharing)