Add option for fetch_benchmark_deps to only fetch needed WPR archives.

Looking at the tryjobs for patchset 4 of this CL (which removes
all WPR archives and redownloads only the ones relevant to the platform
being run), and patchset 10 (which checks baseline, in the mac_chromium_compile_dbg_ng build)
we see the following:

Without change: 791.95s
Android: 104.41s
Win: 189.83s
Mac: 286.69s
Linux: 113s

Change-Id: I5c14eb69cc7f13997910e2759130cdcba9eef5ba
Bug: chromium:1056387
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2425303
Commit-Queue: Ryan Heise <heiserya@google.com>
Auto-Submit: Ryan Heise <heiserya@google.com>
Reviewed-by: John Chen <johnchen@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Cr-Commit-Position: refs/heads/master@{#810397}

DEPS

@@ -4628,17 +4628,53 @@ hooks = [
                 'src/third_party/catapult/telemetry/bin/fetch_telemetry_binary_dependencies',
     ],
   },
-        #
+
   # Download Telemetry's benchmark binary dependencies via conditionals
   {
     'name': 'checkout_telemetry_benchmark_deps',
-    'condition': 'checkout_telemetry_dependencies',
+    'condition': 'checkout_telemetry_dependencies and checkout_linux',
+    'pattern': '.',
+    'action': [ 'vpython',
+                'src/tools/perf/fetch_benchmark_deps.py',
+                '-f',
+                '-p',
+                'linux'
+    ],
+  },
+  {
+    'name': 'checkout_telemetry_benchmark_deps',
+    'condition': 'checkout_telemetry_dependencies and checkout_win',
     'pattern': '.',
     'action': [ 'vpython',
                 'src/tools/perf/fetch_benchmark_deps.py',
                 '-f',
+                '-p',
+                'win'
     ],
   },
+  {
+    'name': 'checkout_telemetry_benchmark_deps',
+    'condition': 'checkout_telemetry_dependencies and checkout_mac',
+    'pattern': '.',
+    'action': [ 'vpython',
+                'src/tools/perf/fetch_benchmark_deps.py',
+                '-f',
+                '-p',
+                'mac'
+    ],
+  },
+  {
+    'name': 'checkout_telemetry_benchmark_deps',
+    'condition': 'checkout_telemetry_dependencies and checkout_android',
+    'pattern': '.',
+    'action': [ 'vpython',
+                'src/tools/perf/fetch_benchmark_deps.py',
+                '-f',
+                '-p',
+                'android'
+    ],
+  },
+
 
   # This is used to ensure that all network operations are properly
   # annotated so we can document what they're for.

tools/perf/fetch_benchmark_deps.py

@@ -17,7 +17,6 @@ from core import benchmark_finders
 from core import path_util
 from py_utils import cloud_storage
 
-
 def _FetchDependenciesIfNeeded(story_set):
   """ Download files needed by a user story set. """
   # Download files in serving_dirs.
@@ -86,6 +85,10 @@ def main(args):
                       help=('Force fetching all the benchmarks when '
                             'benchmark_name is not specified'),
                       action='store_true', default=False)
+  parser.add_argument('--platform', '-p',
+                      help=('Only fetch benchmarks for the specified platform '
+                            '(win, linux, mac, android)'),
+                      default=None)
   # Flag --output-deps: output the dependencies to a json file, CrOS autotest
   # telemetry_runner parses the output to upload the dependencies to the DUT.
   # Example output, fetch_benchmark_deps.py --output-deps=deps octane:
@@ -122,7 +125,11 @@ def main(args):
           'No benchmark name is specified. Fetching all benchmark deps. '
           'Press enter to continue...')
     for b in benchmark_finders.GetOfficialBenchmarks():
-      deps[b.Name()] = _FetchDepsForBenchmark(b)
+      supported_platforms = b.GetSupportedPlatformNames(b.SUPPORTED_PLATFORMS)
+      if(not options.platform or
+         options.platform in supported_platforms or
+         'all' in supported_platforms):
+        deps[b.Name()] = _FetchDepsForBenchmark(b)
 
   if options.output_deps:
     with open(options.output_deps, 'w') as outfile: