Brave-browser: Migrate sync code to Syncable Service

[darkdh]

https://www.chromium.org/developers/design-documents/sync/syncable-service-api

[darkdh]

Test Plan:

1. Test all sync test cases with fresh profile
2. Test all sync test cases launching from legacy sync profile (previous version of Brave which doesn't contain this change)
3. Use new sync device joining existing legacy sync chain (iOS and Android)
4. Use legacy sync device(iOS and Android) joining new sync chain

[btlechowski]

LGTM.

Verified test plan from https://github.com/brave/brave-browser/issues/2754#issuecomment-496602362

sync 0.71.x with 0.71.x
[PASS] Existing bookmarks sync through code words
[PASS] New bookmark sync
[PASS] New folder sync
[PASS] Moved bookmark
[PASS] Moved bookmark folder
[PASS] Deleted bookmark
[PASS] Deleted bookmark folder
[PASS] 5000 bookmarks sync
[PASS] Sync after going offline

sync 0.71.x with 0.68.x
[PASS] Existing bookmarks sync through code words
[PASS] New bookmark sync
[PASS] New folder sync
[PASS] Moved bookmark
[PASS] Moved bookmark folder
[PASS] Deleted bookmark
[PASS] Deleted bookmark folder
[PASS] 5000 bookmarks sync

sync 0.71.x with Android
[PASS] Existing bookmarks sync through QR code
[PASS] New bookmark sync
[PASS] New folder sync
[PASS] Moved bookmark
[PASS] Moved bookmark folder
[PASS] Deleted bookmark
[PASS] Deleted bookmark folder
[PASS] 5000 bookmarks sync

sync 0.71.x with iOS
[PASS] Existing bookmarks sync through QR code
[PASS] New bookmark sync
[PASS] New folder sync
[PASS] Moved bookmark
[PASS] Moved bookmark folder
[PASS] Deleted bookmark
[PASS] Deleted bookmark folder

Also synced multiple devices at once.
Upgraded 0.68.x with existing sync chain to 0.71.x Made sure sync still works.

[bsclifton]

Updated labels for QA + assigned milestone after uplifts were done 😄

@darkdh are there any other issues which were closed out with the uplift? If so, can you help me ID them / also mark them as 0.69.x?

[btlechowski]

Verification passed on

Brave | 0.69.130 Chromium: 77.0.3865.90 (Official Build) (64-bit)
-- | --
Revision | 58c425ba843df2918d9d4b409331972646c393dd-refs/branch-heads/3865@{#830}
OS | Ubuntu 18.04 LTS

Verified Sync part of manual testrun
Verified https://github.com/brave/brave-browser/issues/2754#issuecomment-496602362
Verified https://github.com/brave/brave-browser/issues/2754#issuecomment-524852717

Devices used:
Brave 0.69.130
Brave 0.68.142
Android 1.3.2
iOS 1.12.1

Verified passed with

Brave | 0.69.131 Chromium: 77.0.3865.90 (Official Build) (64-bit)
-- | --
Revision | 58c425ba843df2918d9d4b409331972646c393dd-refs/branch-heads/3865@{#830}
OS | macOS Version 10.13.6 (Build 17G5019)

• Verified Sync part of manual testrun
• Verified basic scenarios from https://github.com/brave/brave-browser/issues/2754#issuecomment-496602362 and https://github.com/brave/brave-browser/issues/2754#issuecomment-524852717
• Verified upgraded sync chain still works
• Verified sync on new profile
• Verified 0.69.x <-> Android (1.4.0) sync, changes were synced across the chain
• Verified 0.69.x <-> iOS (1.12.1) sync, changes were synced across the chain
• Verified 0.69.x <-> Android <-> iOS sync, changes were synced across the chain

Verification passed on

Brave | 0.69.132 Chromium: 77.0.3865.90 (Official Build) (64-bit)
-- | --
Revision | 58c425ba843df2918d9d4b409331972646c393dd-refs/branch-heads/3865@{#830}
OS | Windows 10 OS Version 1803 (Build 17134.1006)

• Verified Sync part of manual testrun
• Verified basic scenarios from https://github.com/brave/brave-browser/issues/2754#issuecomment-496602362 and https://github.com/brave/brave-browser/issues/2754#issuecomment-524852717
• Verified upgraded sync chain still works
• Verified sync on new profile
• Verified 0.69.x <-> Android (1.4.0) sync, changes were synced across the chain
• Verified 0.69.x <-> iOS (1.12.1) sync, changes were synced across the chain
• Verified 0.69.x <-> Android <-> iOS sync, changes were synced across the chain