Reland of Migrate the last optional callbacks to mandatory in Files app's APIs. ...

Reland of Migrate the last optional callbacks to mandatory in Files app's APIs. (patchset #1 id:1 of https://codereview.chromium.org/1230113014/)

Reason for revert:
Relanding as it's not the culprit, I wrongly interpreted sheriff-o-matic ambiguous results.

Sorry for the noise.

Original issue's description:
> Revert of Migrate the last optional callbacks to mandatory in Files app's APIs. (patchset #1 id:1 of https://codereview.chromium.org/1232243005/)
>
> Reason for revert:
> The test is causing browser_tests ExtensionApiTest.CrossOriginXHRNoFileAccess to fail on the Linux Chromium OS Blink bots.
>
> Relevant log:
> [FAIL] fileAccessNotAllowed: expected an error to be thrown
> Error
>     at fileAccessNotAllowed (chrome-extension://dgmgifjgehkiibkkonbjcmcnagdegeco/test.js:24:21)
>     at Object.\u003Canonymous> (extensions::test:95:19)
>     at Object.handleRequest (extensions::binding:57:27)
>     at Object.\u003Canonymous> (extensions::binding:385:32)
>     at Object.\u003Canonymous> (extensions::test:326:16)
>     at Object.handleRequest (extensions::binding:57:27)
>     at Object.\u003Canonymous> (extensions::binding:385:32)
>     at Object.callback (chrome-extension://dgmgifjgehkiibkkonbjcmcnagdegeco/test.js:6:15)
>     at safeCallbackApply (extensions::sendRequest:21:15)
>     at handleResponse (extensions::sendRequest:72:7)", source: chrome-extension://dgmgifjgehkiibkkonbjcmcnagdegeco/test.html (0)
> ../../chrome/browser/extensions/cross_origin_xhr_apitest.cc:37: Failure
> Value of: RunExtensionTestNoFileAccess( "cross_origin_xhr/no_file_access")
>   Actual: false
> Expected: true
>
> Full log of the failure:
> https://build.chromium.org/p/chromium.webkit/builders/Linux%20ChromiumOS%20Tests%20%281%29/builds/17039/steps/browser_tests/logs/ExtensionApiTest.CrossOriginXHRNoFileAccess
>
> Original issue's description:
> > Migrate the last optional callbacks to mandatory in Files app's APIs.
> >
> > TEST=All current tests pass. Closure compiler compiles.
> > BUG=510334
> >
> > Committed: https://crrev.com/5d1f271f25334da3e5a38218f12d48a70d736e53
> > Cr-Commit-Position: refs/heads/master@{#339244}
>
> TBR=fukino@chromium.org,mtomasz@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=510334
>
> Committed: https://crrev.com/6ad0143fab0d1296faf647678f316d8efb0ab0e9
> Cr-Commit-Position: refs/heads/master@{#339260}

TBR=fukino@chromium.org,mtomasz@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=510334

Review URL: https://codereview.chromium.org/1235343005

Cr-Commit-Position: refs/heads/master@{#339269}