Repro:

1. In a non-incognito tab, visit https://example.com
2. Go to DevTools > Application > Clear storage
3. Note amount of quota available (should be roughly 6% of disk size, with current heuristics - e.g. a GB if you're on a modern machine)
4. In an incognoto tab, visit https://example.com
5. Go to DevTools > Application > Clear storage
6. Note amount of quota available is far less than in #3 (e.g. 100MB)

Since incognito storage uses memory rather than disk we cap the size. But developers often test in incognito and may be surprised that the limit is so low when we say that sites can use a lot more.

Note that we don't want to train developers to expect certain values, and there's not a hard limit (otherwise sites could use it to probe for incognito).

Suggestion: show a bit of text below the storage indicator, e.g. "(storage is limited in incognito sessions)"