go/types: fix missing Importer for TestBenchmark
go/types: fix missing Importer for TestBenchmark

TestBenchmark is broken due to lack of a Config.Importer, but
unfortunately fails silently due to an unchecked error.

Fix the importer and check the error. Also improve the output to include
allocation stats.

Finally, don't run TestBenchmark on go/types by default. If the
benchmark is being used during a refactoring of go/types itself, results
for go/types will not be comparable.

Change-Id: Ib6bdb6807403b3ec99762f535e2496c94bd9b6e0
Reviewed-on: https://go-review.googlesource.com/c/go/+/249517
Run-TryBot: Robert Findley <9179eee875d1ee628c37fb47d7e749e855ffd21f@google.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Alan Donovan <7069e9552f9d110b0a0f326b96f22f63fb99dfc1@google.com>

golang/go,nawawi/go,nawawi/go,golang/go,CAFxX/go,CAFxX/go,golang/go,CAFxX/go,golang/go,nawawi/go,CAFxX/go,nawawi/go,CAFxX/go,golang/go,golang/go,nawawi/go,cloudflare/go,golang/go,golang/go,nawawi/go,CAFxX/go,cloudflare/go,cloudflare/go,cloudflare/go,CAFxX/go,nawawi/go,cloudflare/go,cloudflare/go,nawawi/go,cloudflare/go,cloudflare/go,CAFxX/go