Extension popups crash browser

[petemill]

Test plan

1. Enable metamask extension
2. Click metamask extension icon
3. Ensure browser doesn't crash

Description

Basic Non-tab <webview src="x"> elements are not loading any contents. These are used in extension popups which also cause a crash.

Steps to Reproduce

1. Enable metamask extension
2. Click metamask extension icon

Actual result:
Crash

Expected result:
Loads popup (invisible on first time, visible on second time, like release)

Reproduces how often:
100%

Brave Version

about:brave info:
0.22.109

Reproducible on current live release:
No

[petemill]

Should be fixed with muon 6.0.6

[srirambv]

Verified on Windows x64

• 0.22.702 e4a853d
• libchromiumcontent 66.0.3359.139
• muon: 6.0.7

Verified with macOS 10.12.6 using

• 0.22.702 e4a853d
• muon 6.0.7
• libchromiumcontent 66.0.3359.139
• Also encountered Extension popups empty and transparent on first click after Brave restart #13633 when testing this

Verified on Mint 18.3 x64 using the following build:

• 0.22.702 e4a853d
• Muon: 6.0.7
• libchromiumcontent: 66.0.3359.139
• also ran into Extension popups empty and transparent on first click after Brave restart #13633 when going through this issue with MetaMask.