Code views unreliably detected on large PRs

Created by: lguychard

• Visit a PR with many files changed, for instance https://github.com/sourcegraph/sourcegraph/pull/2838/files
• Witness not all code views have "view file" button initially

• If you scroll down too quickly, code views will not be detected.
• If you scroll up/down some more, eventually the code views will all be detected.

I believe this is due to emitWhenIntersecting()