Memory leak in plugins?

[kroikie]

So, I may be wrong, but in the plugins below it looks like that registration in the ActivityLifecycleCallbacks and in the LocalBroadcastManager may become memory leaks in case the Flutter Activity is open multiple times.
For instance, when flutter is being used in add-to-app to show a product detail. Every time that Activity is open the plugin registration process is triggered and a new listener is attached, but it is never released.

https://github.com/flutter/plugins/blob/master/packages/firebase_messaging/android/src/main/java/io/flutter/plugins/firebasemessaging/FirebaseMessagingPlugin.java#L58

https://github.com/flutter/plugins/blob/master/packages/image_picker/android/src/main/java/io/flutter/plugins/imagepicker/ImagePickerPlugin.java#L95

https://github.com/flutter/plugins/blob/master/packages/google_maps_flutter/android/src/main/java/io/flutter/plugins/googlemaps/GoogleMapsPlugin.java#L36

I have some ideas of how to avoid those calls, but I would like to confirm this before trying to change the code.

[iapicca]

#53
#766
#829
#508