Introduce TracingController and TracingControllerBackend skeleton

tools/telemetry/telemetry/core/platform/tracing_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.
+
+class TracingController(object):
+  def __init__(self, tracing_controller_backend):
+    """Provides control of the tracing systems supported by telemetry."""
+    self._tracing_controller_backend = tracing_controller_backend
+
+  def Start(self, category_filter, trace_options, timeout=10):
+    """Starts tracing.
+
+    trace_options specifies which tracing systems to activate. Category filter
+    allows fine-tuning of the data that are collected by the selected tracing
+    systems.
+    """

[nednguyen, 2014/08/04 22:12:06]

Should we add assert self.AreOptionsSupported(trace_options) here?

+    self._tracing_controller_backend.Start(
+        category_filter, trace_options, timeout)
+
+  def Stop(self):
+    """Stops tracing and returns a TraceValue."""
+    return self._tracing_controller_backend.Stop()
+
+  @property
+  def is_tracing_running(self):
+    return self._tracing_controller_backend.is_tracing_running
+
+  def AreOptionsSupported(self, trace_options):
+    """Returns whether the tracers requested by trace_options are supported.
+
+    If the browser is not running at the time that this query is issued, then
+    no answer can be provided.
+    """
+    return self._tracing_controller_backend.AreOptionsSupported(trace_options)