Adds restart method and auxiliar callback to polling class
What does this MR do?
According to the discussion in this MR: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/10210
- Adds restart method so we can start polling again after visibility changes back.
- Adds notifiction callback so we can know outside the polling class that we are making a request. This will allow to prevent scenarios where we would make 2 requests at the same time.
- Parses received header into a number.
These changes were moved into this MR so @selfup can use them at the same time and not be blocked
Does this MR meet the acceptance criteria?
- Tests
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Added for this feature/bug -
All builds are passing
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Conform by the merge request performance guides -
Conform by the style guides -
Branch has no merge conflicts with master(if it does - rebase it please)