telemetry: Add 'webkit' category back to smoothness benchmark.

We still need the 'webkit' category in the trace until the reference
build is updated to a revision that uses 'webkit.console' for the timeline
markers.

R=tonyg@chromium.org
BUG=282712

Review URL: https://chromiumcodereview.appspot.com/23757054

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@223477 0039d316-1c4b-4281-b951-d872f2087c98

tools/perf/measurements/smoothness.py

@@ -44,7 +44,9 @@ class Smoothness(page_measurement.PageMeasurement):
     return hasattr(page, 'smoothness')
 
   def WillRunAction(self, page, tab, action):
-    tab.browser.StartTracing('webkit.console,benchmark', 60)
+    # TODO(ermst): Remove "webkit" category after Blink r157377 is picked up by
+    # the reference builds.
+    tab.browser.StartTracing('webkit,webkit.console,benchmark', 60)
     if tab.browser.platform.IsRawDisplayFrameRateSupported():
       tab.browser.platform.StartRawDisplayFrameRateMeasurement()
     self._metrics = smoothness.SmoothnessMetrics(tab)