Nominate a specific, canonical extension for pprof files

Hi, over on internal bug b/487062289 I'm working on benchmarks that output a .pprof file into sponge.

I'd like to have a button where you can click from the benchmark results to go to the pprof web UI. We already have this for Perfetto, it's nice.

I need to match for pprof files. For Perfetto, we have a PerfettoMatchUtil.java:

  private static final ImmutableSet<String> PERFETTO_EXTENSIONS =
      ImmutableSet.of(
          ".pftrace.gz", // UTP Perfetto Plugin
          ".pftrace",
          "_perfetto.pb.gz",
          "_perfetto.pb",
          ".perfetto-trace.gz", // Extension used in Perfetto docs
          ".perfetto-trace");

It's a bit of a mess (indicating they could have chosen a canonical extension earlier), but it works.

I'd like a canonical, distinguishing file extension for pprof profiles. But I need a file extension matcher that doesn't give me too many false positives.

There's a lot of talk in pprof about outputting .pb and .pb.gz. These are perhaps canonical, but not distinct from the myriad other wireformat protocol buffer formats.

Not distinct enough to offer a 'open in pprof' link from generic testing infrastructure; they'd probably have too many false positives.

I propose we just declare that pprof files canonically use extensions:

• foo.pprof
• foo.pprof.gz

And we update the docs that talk about .pb .pb.gz to use these as examples.

Thoughts?