Telemetry: fix image decoding category to follow blink change once again

This adds disabled-by-default-devtools.timeline* to the category filter
to follow the new category name pattern used by timeline on the blink
side. See also: https://codereview.chromium.org/337143002

BUG=381548

Review URL: https://codereview.chromium.org/334293002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@278023 0039d316-1c4b-4281-b951-d872f2087c98

tools/perf/measurements/image_decoding.py

@@ -25,7 +25,10 @@ class ImageDecoding(page_measurement.PageMeasurement):
         }
     """)
     self._power_metric.Start(page, tab)
-    tab.browser.StartTracing('devtools,webkit.console')
+    # FIXME: bare 'devtools' is for compatibility with older reference versions
+    # only and may eventually be removed.
+    tab.browser.StartTracing(
+        'disabled-by-default-devtools.timeline*,devtools,webkit.console')
 
   def StopBrowserAfterPage(self, browser, page):
     return not browser.tabs[0].ExecuteJavaScript("""