[AF] Deprecates autofill::prefs::kAutofillEnabled

Deprecates kAutofillEnabled in favor of finer grained
kAutofillProfileEnabled and kAutofillCreditCardEnabled

Keeps kAutofillEnabled around to maintain backward compatibility for the
extensions and the policy APIs. If kAutofillEnabled is set by an extension,
values of kAutofillProfileEnabled and  kAutofillCreditCardEnabled are also
set. Similarly, if kAutofillEnabled is disabled by policy, the two
fine-grained prefs are also disabled.

Chrome extension for testing the chrome.privacy.services API:
https://github.com/mhahmadi/autofill-pref-api-test-extension

TBR=michaelbai@

Bug: 870328, 860526
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I8e6ca4594aa73c3d9228734948353f6a686227ad
Reviewed-on: https://chromium-review.googlesource.com/1166211
Commit-Queue: Moe Ahmadi <mahmadi@chromium.org>
Reviewed-by: Tao Bai <michaelbai@chromium.org>
Reviewed-by: Moe Ahmadi <mahmadi@chromium.org>
Reviewed-by: Maksim Ivanov <emaxx@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Reviewed-by: Vadym Doroshenko <dvadym@chromium.org>
Reviewed-by: John Wu <jzw@chromium.org>
Reviewed-by: Sebastien Seguin-Gagnon <sebsg@chromium.org>
Reviewed-by: Mathieu Perreault <mathp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#582936}
22 files changed