Sync should handle library/client errors

[cezaraugusto]

Sync should handle library/client errors. We have this mechanism in the back-end but interface should be aware of it.

The error happens when sync client (browser) can't connect with the sync server for N reasons, so the message needs to be generic.

Worth mentioning that the offline error is already handled so this is different.

cc @rebron @bradleyrichter to cook a good phrase for this.

Test Plan:

1. Create a sync chain and ensure you see two devices
2. Quit Brave
3. Launch Brave without internet
4. You should see a Couldn't contact Sync servers error dialog

[rebron]

#1149 related issue.

I think we can go with something like:

Title: Sync servers can't be reached
Body: The sync servers might temporarily be down. Please try again later.

cc: @tomlowenthal

[tildelowengrimm]

[Always blame the user 😛]
Title: Couldn't contact Sync servers
Body: You might be having network trouble, or there could be a problem with the Sync servers.

[srirambv]

Marking as QA/Yes as this requires text verification.

[rebron]

@cezaraugusto can we get this in for 58.x too? Use toml text above/repeated here:
Title: Couldn't contact Sync servers
Body: You might be having network trouble, or there could be a problem with the Sync servers.

Can you also create a test plan for QA.

[cezaraugusto]

sure I'll be addressing this in a quick follow-up once sync v2 lands

[LaurenWags]

@cezaraugusto - in the test plan, should we see the error just by navigating to brave://sync or do we need to perform an action on the page (View Sync Code, Leave Sync Chain, Add Device, etc)?

[GeetaSarvadnya]

@cezaraugusto Verified the issue on 0.59.12. I am not seeing Couldn't contact Sync servers error dialog

[GeetaSarvadnya]

Verification passed on

Brave	0.59.14 Chromium: 72.0.3626.28 (Official Build) beta (64-bit)
Revision	997b1040b63bac324e815797ba52be0cd8f616ed-refs/branch-heads/3626@{#461}
OS	Windows

• Verified the STR from description

Verified passed with

Brave	0.59.14 Chromium: 72.0.3626.28 (Official Build) beta(64-bit)
Revision	997b1040b63bac324e815797ba52be0cd8f616ed-refs/branch-heads/3626@{#461}
OS	Mac OS X

• Verified test plan from description
  

Verification passed on

Brave	0.59.14 Chromium: 72.0.3626.28 (Official Build) beta(64-bit)
Revision	997b1040b63bac324e815797ba52be0cd8f616ed-refs/branch-heads/3626@{#461}
OS	Linux

Used test plan from description
Logged #2814