Sync code modal is not dismissed when trying to enable sync offline

[srirambv]

• Did you search for similar issues before submitting this one?
  yes

• Describe the issue you encountered:
  Sync code modal is not dismissed when trying to enable sync offline

• Platform (Win7, 8, 10? macOS? Linux distro?):
  Windows x 64

• Brave Version (revision SHA):
  Brave 0.15.0
  rev 6638b91

• Steps to reproduce:

  1. Open about:preferences#sync
  2. Click on I have a existing code to bring the modal
  3. Enter the sync code
  4. Disconnect system from network
  5. Click on Setup Sync
  6. Sync fails but the modal still shows up

• Actual result:
  Sync code modal is not dismissed when trying to enable sync offline

• Expected result:
  Modal should not be shown

• Will the steps above reproduce in a fresh profile? If not what other info can be added?
  Yes

• Is this an issue in the currently released version?
  Not tested

• Can this issue be consistently reproduced?
  Yes

• Extra QA steps:
  1.
  2.
  3.

• Screenshot if needed:
  

• Any related issues:
  Please change milestone if required

[diracdeltas]

kicking to a later milestone since it is an edge case for the network to disconnect while the modal is open

[alexwykoff]

migrated to brave/sync#115