[Chromium] Sometimes web pages may not be cleaned up properly after launch

[gorhill]

Case:

1. uBlock's _"3rd-party filters": purge all caches -- this is just to force a slower reload of all filters at launch)
2. Have a single tab in the browser
3. Google "buy iphone" (a sure way to get results with ads)
4. Quit the browser
5. Launch the browser
6. Sometimes the "buy iphone" tab will open and the ads in it won't be mopped up by uBlock

This happens when uBlock's main process is not ready fast enough to report the proper set of filters when the content scripts query for them. The manual injection of the content scripts was supposed to take care of this, but some code added in a previous bug fixed caused the manually injected scripts to become a noop sometimes.

[gorhill]

This was fix in 673b877. I opened the issue just so we have a track record of the regression.