Convert Callback to {Once,Repeating}Callback in //content/browser.

Use OnceCallback where possible, and use BindRepeating() where it is
meant to be a RepeatingCallback.

Majority of this change is a few typedefs that are very widely used:
- LoadedCallback
- ValidateTokenCallback
- ValidateRegistrationCallback
- GotDataCallback**

** Especially this one.

[email protected], [email protected], [email protected]
TBR=clamy

Bug: 1007760
Change-Id: I3e6b2bfbc1ff5d36a96628da1163f6a37fb2b204
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1943327
Commit-Queue: danakj <[email protected]>
Reviewed-by: Mark Cogan <[email protected]>
Reviewed-by: Colin Blundell <[email protected]>
Cr-Commit-Position: refs/heads/master@{#720205}
145 files changed