Introduce TracingController and TracingControllerBackend skeleton

tools/perf/measurements/timeline_controller.py

Index: tools/perf/measurements/timeline_controller.py
diff --git a/tools/perf/measurements/timeline_controller.py b/tools/perf/measurements/timeline_controller.py
index 4cd0008b27de9fea89ba7ebe66f8e1593da1855e..27a1ac63cdc4d02db99ac263dbb031f2bc1d04b9 100644
--- a/tools/perf/measurements/timeline_controller.py
+++ b/tools/perf/measurements/timeline_controller.py
@@ -3,7 +3,7 @@
 # found in the LICENSE file.
 from measurements import smooth_gesture_util
 
-from telemetry.core.backends.chrome import tracing_backend
+from telemetry.core.platform import tracing_category_filter
 from telemetry.timeline.model import TimelineModel
 from telemetry.page.actions import action_runner
 from telemetry.web_perf import timeline_interaction_record as tir_module
@@ -15,7 +15,7 @@ RUN_SMOOTH_ACTIONS = 'RunSmoothAllActions'
 class TimelineController(object):
   def __init__(self):
     super(TimelineController, self).__init__()
-    self.trace_categories = tracing_backend.DEFAULT_TRACE_CATEGORIES
+    self.trace_categories = None
     self._model = None
     self._renderer_process = None
     self._smooth_records = []
@@ -30,12 +30,11 @@ class TimelineController(object):
     self._renderer_process = None
     if not tab.browser.supports_tracing:
       raise Exception('Not supported')
-    if self.trace_categories:
-      categories = [self.trace_categories] + \
-          page.GetSyntheticDelayCategories()
-    else:
-      categories = page.GetSyntheticDelayCategories()
-    tab.browser.StartTracing(','.join(categories))
+    category_filter = tracing_category_filter.TracingCategoryFilter(
+        filter_string=self.trace_categories)
+    for delay in page.GetSyntheticDelayCategories():
+      category_filter.AddSyntheticDelay(delay)
+    tab.browser.StartTracing(category_filter)
 
   def Start(self, tab):
     # Start the smooth marker for all actions.