Update media_router_perf_tests to run with the script in correct location.

Bug: 968849
Change-Id: Ie21bb36c547d5ce661cb031b58c9f6ffe7ce692f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1637529
Commit-Queue: Clifford Cheng <cliffordcheng@chromium.org>
Reviewed-by: Marc-Antoine Ruel <maruel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#665014}

testing/buildbot/gn_isolate_map.pyl

@@ -1544,7 +1544,7 @@
       "--output-dir=${ISOLATED_OUTDIR}",
     ],
     "label": "//chrome/test/media_router:media_router_perf_tests",
-    "script": "//chrome/test/media_router/telemetry/run_benchmark.py",
+    "script": "//tools/perf/contrib/media_router_benchmarks/run_benchmark.py",
     "type": "script",
   },
   "media_service_unittests": {