[Extensions Callback Cleanup] RouteHandlerFunction

Do the following clean-ups in
ObjectBackedNativeHandler::RouteHandlerFunction() and its callers:
- Convert base::Callback to base::RepeatingCallback/base::OnceCallback
- Convert base::Bind to base::BindRepeating/base::BindOnce
- Pass callbacks by value when an instance is retained

In practice, these are all base::RepeatingCallbacks.

Bug: 714018
Change-Id: I5c7c58bcad7d033ca576ff7bde173bc6f9482303
Reviewed-on: https://chromium-review.googlesource.com/c/1391853
Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619779}
44 files changed