11% npm install speed increase: add caching to fromUrl

[mikesherov]

TL:DR

~11% speed up in the average npm install run

Details

You would not believe how often fromUrl gets hit in the average npm i run. On a fairly large private project that installs 1764 packages, if I track number of cache hits and misses, I get:

Hit rate:

miss 5713
hit  240941

This translates to build times (w package-lock.json but without a node_modules dir, which is common in CI runs) of:

Before:

added 1764 packages in 51.943s
added 1764 packages in 51.135s
added 1764 packages in 50.688s
added 1764 packages in 52.048s
added 1764 packages in 52.156s
added 1764 packages in 54.817s

After

added 1764 packages in 46.1s
added 1764 packages in 47.784s
added 1764 packages in 49.382s

[iarna]

The unbounded nature of this cache makes me a bit nervous, but I'm ok taking this until and if memory profiling points to change.

[mikesherov]

Thanks, I had a similar concern, but believe it or not, it was only slightly more memory than without the cache, presumably because of lots of memory thrashing due to unbounded object creation in npm proper.

If it ends up being a bigger deal, we can jam lru-cache on it, as you're suggesting.

Thanks for merging!