[testing] Abstract and apply memory usage testing across the repo

[Westbrook]

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Code of conduct

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Description of issue

Building off of #3721, abstract the usage of measureUserAgentSpecificMemory() to a test helper, and apply that helper across all of the packages in the project.

Address leaks, etc., as they are uncovered.

[Westbrook]

Questions to answer:

• is it safe to run this "flag-customized" version of chromium for all tests? or should you create a group config using it that focuses only on the grid memory tests?

[Westbrook]

Not complete yet. But good progress.