In PackageBuilder._discoverLibraries, initialize newFiles outside loop.

[srawlins]

I noticed with print debugging that addFilesReferencedBy was being called way too many times for a given library. It turns out this is because it was being called on different Sets, when really it should mostly be operating on one Set. That one Set is newFiles. It was initialized in the do-while loop, but it can be initialized before the do-while loop.

I checked the logic to make sure this change is a no-op.

I also timed documenting flutter. This change seems to reduce the time-to-document by ~100 seconds, but that is only with one before and one after, so I promise nothing.

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[kallentu]

I also timed documenting flutter. This change seems to reduce the time-to-document by ~100 seconds, but that is only with one before and one after, so I promise nothing.

If this is truly the case, I'm shocked.

[srawlins]

If this is truly the case, I'm shocked.

Haha, I promise nothing! 100 seconds probably isn't within the margin of error, but it could be a much smaller improvement on average.