Addressbar displays hidden extensions URL for new tab

[btlechowski]

Test plan

See #14239 (comment)

Steps to Reproduce

1. Clean profile
2. Press + for new tab

Actual result:
Addressbar displays chrome-extension://mnojpmjdmbbfmejpflffifhffcmidifd/about-newtab.html

Expected result:
After new tab adressbar is empty

Reproduces how often:
100%

Brave Version

Brave: 0.22.801 
V8: 6.7.288.33 
rev: 6ec9f53d0178df2d614e6d92597f1d7762d33ce6 
Muon: 7.0.0 
OS Release: 4.13.0-21-generic 
Update Channel: Beta 
OS Architecture: x64 
OS Platform: Linux 
Node.js: 7.9.0 
Brave Sync: v1.4.2 
libchromiumcontent: 67.0.3396.48

@LaurenWags and @kjozwiak reported that this is not reproducible on MacOS

Reproducible on current live release:
No

cc @bsclifton @petemill @bridiver

[srirambv]

Not reproducible on Windows.

Edit: Reproduced on Windows with a webview crash in a tab and the click on the new tab button. Doesn't always happen though

Edit 2: Able to consistently see the URL on new tab on Windows as well no idea whats triggering it but shows up on each tab

[LaurenWags]

Was able to reproduce on macOS with these STR:
Add a tab, enter a URL and hit return.
While the tab is loading the page, quickly (very quickly) use cmd+t to open a new tab.
New tab opens and URL bar shows chrome-extension://mnojpmjdmbbfmejpflffifhffcmidifd/about-newtab.html

[hferreiro]

The issue seems to be fixed after brave/muon@8868bc4, which was pushed after the release.

[srirambv]

Verified on Windows x64 using

• 0.22.806 0d30970
• muon 7.0.3
• libchromiumcontent 67.0.3396.62

Verified with macOS 10.12.6 using

• 0.22.806 0d30970
• Muon 7.0.3
• libchromiumcontent 67.0.3396.62

Verified on Ubuntu 17.10 x64

• 0.22.806 0d30970
• Muon 7.0.3
• libchromiumcontent 67.0.3396.62