Add context to wrapped function

[fatso83]

Summary

• Fix Unsure how / no way to replace methods with fakes #1850 by keeping this context
• Added a regression test to verify it.

How to verify

1. Check out this branch
2. npm install
3. npm test - see the test added in the first commit pass

• npm run lint passes
• References to standard library functions are cached.

[coveralls]

Pull Request Test Coverage Report for Build 2680

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 95.356%

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Totals
Change from base Build 2673:	0.0%
Covered Lines:	2043
Relevant Lines:	2097

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💛 - Coveralls

[fatso83]

For some reason crashed in the webworker test on Node 10, but no other versions ... Weird, since it doesn't actually run on Node, but in chromium.

[fatso83]

@fearphage This fails on the unstable Chrome version. Works fine on stable Google Chrome 65.0.3325.162 (Linux). Any idea why we are not running on the stable branch? I remember you setting it up, but I don't remember any details. I suspect this being the culprit:

npm run test-webworker -- --chrome $(which google-chrome-unstable) --allow-chrome-as-root

[mantoni]

@fatso83 Stable chrome install doesn't succeed in docker containers. Not sure if / when this will be supported in the regular version.

[fatso83]

Made it work by installing both stable and unstable. Needed both - unstable for headless and stable for WebWorker ...