Update webrtc smoothness metric category

These categories were renamed in a previous CL. This fix the corresponding
telemetry test.

Bug: 837881
Change-Id: I0c769add6d9a78ce1364983ed5bb70ac0d644ee0
Reviewed-on: https://chromium-review.googlesource.com/1034119Reviewed-by: Patrik Höglund <phoglund@chromium.org>
Reviewed-by: Annie Sullivan <sullivan@chromium.org>
Commit-Queue: Emircan Uysaler <emircan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#554855}

tools/perf/benchmarks/webrtc.py

@@ -27,7 +27,7 @@ class WebrtcPerfBenchmark(perf_benchmark.PerfBenchmark):
         '-*',
         'toplevel',
         # WebRTC
-        'webmediaplayerms',
+        'media',
     ]
 
     category_filter = chrome_trace_category_filter.ChromeTraceCategoryFilter(