Remove start & stop logic from timeline_metric.

tools/perf/measurements/timeline_controller.py

+# Copyright 2014 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+import itertools
+
+from telemetry.core.timeline.model import TimelineModel
+
+# All tracing categories not disabled-by-default
+DEFAULT_TRACE_CATEGORIES = None
+
+# Categories for absolute minimum overhead tracing. This contains no
+# sub-traces of thread tasks, so it's only useful for capturing the
+# cpu-time spent on threads (as well as needed benchmark traces)
+MINIMAL_TRACE_CATEGORIES = ("toplevel,"
+                            "benchmark,"
+                            "webkit.console,"
+                            "trace_event_overhead")
+
+
+class TimelineController(object):
+  def __init__(self):
+    super(TimelineController, self).__init__()
+    self.trace_categories = DEFAULT_TRACE_CATEGORIES
+    self._model = None
+    self._renderer_process = None
+    self._actions = []
+    self._action_ranges = []
+
+  def Start(self, page, tab):
+    """Starts gathering timeline data.
+
+    """
+    # Resets these member variables incase this object is reused.
+    self._model = None
+    self._renderer_process = None
+    self._actions = []
+    self._action_ranges = []
+    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))
+
+  def Stop(self, tab):
+    timeline_data = tab.browser.StopTracing()
+    self._model = TimelineModel(timeline_data)
+    self._renderer_process = self._model.GetRendererProcessFromTab(tab)
+    self._action_ranges = [ action.GetActiveRangeOnTimeline(self._model)
+                            for action in self._actions ]
+    # Make sure no action ranges overlap
+    for combo in itertools.combinations(self._action_ranges, 2):
+      assert not combo[0].Intersects(combo[1])
+
+  def AddActionToIncludeInMetric(self, action):
+    self._actions.append(action)
+
+  @property
+  def model(self):
+    return self._model
+
+  @property
+  def renderer_process(self):
+    return self._renderer_process
+
+  @property
+  def action_ranges(self):
+    return self._action_ranges