enable developer mode using browser

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Welcome! Plese use this template for reporting documentation issues on https://developers.google.com/web/.

For questions about Chrome DevTools, checkout the google-chrome-devtools tag on StackOverflow. For questions about Chrome, check the google-chrome tag. If you think you've found a Chrome bug, check out our feedback page for more details on how to file it.

Page Affected: https://developers.google.com/web/TODO

What needs to be done?

Please provide description of what's needs to be done here. Please be sure to include the link to the original page and any supporting links/data.

• [ ] Appropriate type-something label has been added.
• [ ] Appropriate section-something label has been added.