Fix#20125: Convert string to regex.

[rahat2134]

Overview

1. This PR fixes or fixes part of #20125
2. This PR does the following: There was an error in console occuring. When using Puppeteer to preview documents via Google Docs Viewer in Node.js, the browser throws an error. Despite the URL working well in a browser environment, attempting to access it through Puppeteer results in an error. Set that error to ignore because it was from external factors and breaking the tests.

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[oppiabot[bot]]

Assigning @StephenYu2018 for the first pass review of this PR. Thanks!

[rahat2134]

Don't know why mypy checks are failing. I think there is something due to current branch which I restored. Opening new PR with new branch. This branch was deleted from my local machine and I think that is causing error.