Reland #2 of "Parallelize fetching telemetry benchmark deps"

This reverts commit e6ad8b42.

Difference from previous reland: using close and join instead of terminate

Original change's description:
> Revert "Reland "Parallelize fetching telemetry benchmark deps""
>
> This reverts commit 95e22d39.
>
> Reason for revert: Potentially breaking many builders, https://crbug.com/1108314
>
> Original change's description:
> > Reland "Parallelize fetching telemetry benchmark deps"
> >
> > This is a reland of 8ab0b856
> >
> > Original change's description:
> > > Parallelize fetching telemetry benchmark deps
> > >
> > > The fetching script currently fetches about 2 GB (on my linux workstation)
> > > from cloud storage serially. This can (and is) trivially parallelizable, and
> > > should speed up the fetching script significantly.
> > >
> > > This script has been taking 20 minutes on mac machines for a long time. This
> > > will hopefully significantly speed the mac builders up.
> > >
> > > Bug: 1102597
> > > Change-Id: I93d2fa2b1f4b4ef6e27e9c894a9dd4c0d0e12d7b
> > > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2285503
> > > Commit-Queue: Stephen Martinis <martiniss@chromium.org>
> > > Reviewed-by: Wenbin Zhang <wenbinzhang@google.com>
> > > Reviewed-by: John Chen <johnchen@chromium.org>
> > > Cr-Commit-Position: refs/heads/master@{#786521}
> >
> > Bug: 1102597
> > Change-Id: I37d0055fadb26bf4eae2b0b5fe0ecc4732edde3d
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2288740
> > Commit-Queue: Stephen Martinis <martiniss@chromium.org>
> > Reviewed-by: John Chen <johnchen@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#789736}
>
> TBR=martiniss@chromium.org,johnchen@chromium.org,wenbinzhang@google.com
>
> # Not skipping CQ checks because original CL landed > 1 day ago.
>
> # Tree is currently closed, trying to fix an outage
>
> No-Try: true
> No-Tree-Checks: true
> Bug: 1102597
> Change-Id: If6b95395208a3136a798118e4eb229e4322c7878
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2317774
> Commit-Queue: Stephen Martinis <martiniss@chromium.org>
> Reviewed-by: Stephen Martinis <martiniss@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#791304}

TBR=martiniss@chromium.org,johnchen@chromium.org,wenbinzhang@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1102597
Change-Id: I2f9a7162e73ee264ed9f0f844f45106160bce793
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2339589
Commit-Queue: Stephen Martinis <martiniss@chromium.org>
Reviewed-by: Stephen Martinis <martiniss@chromium.org>
Reviewed-by: Wenbin Zhang <wenbinzhang@google.com>
Cr-Commit-Position: refs/heads/master@{#795751}

tools/perf/fetch_benchmark_deps.py

@@ -7,10 +7,11 @@
 
 import argparse
 import json
+import logging
+import multiprocessing
 import optparse
 import os
 import sys
-import logging
 
 from chrome_telemetry_build import chromium_config
 from core import benchmark_finders
@@ -121,8 +122,13 @@ def main(args):
       raw_input(
           'No benchmark name is specified. Fetching all benchmark deps. '
           'Press enter to continue...')
-    for b in benchmark_finders.GetOfficialBenchmarks():
-      deps[b.Name()] = _FetchDepsForBenchmark(b)
+    benchmarks = benchmark_finders.GetOfficialBenchmarks()
+    p = multiprocessing.Pool()
+    results = p.map(_FetchDepsForBenchmark, benchmarks)
+    p.close()
+    p.join()
+    for benchmark, result in zip(benchmarks, results):
+      deps[benchmark.Name()] = result
 
   if options.output_deps:
     with open(options.output_deps, 'w') as outfile: