Disable Phone/Computer buttons until the device name is queried

[srirambv]

Test plan

See brave/brave-core#1193

Description

Disable Phone/Computer buttons until the device name is queried

Steps to Reproduce

1. Install 0.60.4
2. Enable Sync via hamburger menu or via brave://sync
3. Wait for the device name to be queried. Time varies, sometime its instatnaeous and sometime there is a considerable delay
4. UI shows Let’s sync a new device with “”. while its being queried
5. Click on Computer, doesn't show the code words
6. Click on Phone/Tablet doesn't show the QR code
7. Close and reopen brave://sync, device name is instantly queried and you can see the QR/code words with appropriate option being selected

Actual result:

https://youtu.be/P4_vqKroqHc

Expected result:

Should query device name instantly and the computer/phone/tablet buttons should be inactive if there is a delay in getting the device name

Reproduces how often:

Easy

Brave version (brave://version info)

Brave	0.60.4 Chromium: 72.0.3626.17 (Official Build) dev(64-bit)
Revision	08d2140079f8db14c9eb885a803d231b1a30e817-refs/branch-heads/3626@{#315}
OS	Linux

Reproducible on current release:

• Does it reproduce on brave-browser dev/beta builds?
  Yes

Website problems only:

• Does the issue resolve itself when disabling Brave Shields?
  N/A
• Is the issue reproducible on the latest version of Chrome?
  N/A

Additional Information

cc: @bradleyrichter for design input
@rebron @brave/legacy_qa

[srirambv]

Verification passed on

Brave	0.59.20 Chromium: 72.0.3626.28 (Official Build) beta(64-bit)
Revision	997b1040b63bac324e815797ba52be0cd8f616ed-refs/branch-heads/3626@{#461}
OS	Linux

• Verified new UI doesn't show the quering of device name. The waiter message takes time to add the second device to chain which is good enough time to get the device name

Verification passed on

Brave	0.59.20 Chromium: 72.0.3626.28 (Official Build) beta (64-bit)
Revision	997b1040b63bac324e815797ba52be0cd8f616ed-refs/branch-heads/3626@{#461}
OS	Windows 10

• Verified new UI doesn't show the quering of device name. The waiter message takes time to add the second device to chain which is good enough time to get the device name

Verified passed with

Brave	0.59.20 Chromium: 72.0.3626.28 (Official Build) beta(64-bit)
Revision	997b1040b63bac324e815797ba52be0cd8f616ed-refs/branch-heads/3626@{#461}
OS	Mac OS X

• Verified test plan for this issue from fix multiple sync issues brave-core#1193