I suggest using snappy-debug for pastes (the recent upload has a lot of nice improvements).
For dconf, you need to plugs the gsettings interface.
For the ‘ptrace’ syscall, this is not covered by process-control. ptrace can be used to break out of the seccomp sandbox in kernels < 4.8. However, I suspect this was triggered due to cascading failures (ie, if the shm accesses were allowed, we could allow it).
The shm denials are covered here: Shared memory in /dev/shm rewriting. Does using the snapcraft preload part resolve this? If it does, that is the ideal solution. If it doesn’t, we can consider updating the browser-support interface (it looks like nwjs uses the chromium content api under the hood).