Use correct argument for benchmark name.

See https://cs.chromium.org/chromium/src/testing/scripts/run_performance_tests.py?l=201

I used the wrong arg in
https://chromium-review.googlesource.com/c/chromium/src/+/1428090
but it didn't break because the logic doesn't yet require this
argument.

BUG=924351

Change-Id: I69f7fc5bfbd01537f8d99ace53b64d73386bf96f
Reviewed-on: https://chromium-review.googlesource.com/c/1433292
Auto-Submit: Caleb Rouleau <crouleau@chromium.org>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Commit-Queue: Caleb Rouleau <crouleau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625765}

testing/buildbot/gn_isolate_map.pyl

@@ -649,7 +649,7 @@
   "components_perftests": {
     "args": [
       "--xvfb",
-      "--benchmark=components_perftests",
+      "--gtest-benchmark-name=components_perftests",
       "--non-telemetry=true",
       "--migrated-test=true",
       "components_perftests",
@@ -2578,7 +2578,7 @@
   "views_perftests": {
     "args": [
       "--xvfb",
-      "--benchmark=views_perftests",
+      "--gtest-benchmark-name=views_perftests",
       "--non-telemetry=true",
       "--migrated-test=true",
       "views_perftests",