[Telemetry] Re-add API to tear down state after each story run

telemetry/telemetry/testing/fakes/__init__.py

Index: telemetry/telemetry/testing/fakes/__init__.py
diff --git a/telemetry/telemetry/testing/fakes/__init__.py b/telemetry/telemetry/testing/fakes/__init__.py
index 06e9aa7b30fb3cd78eac2bbe53139a29c37e5a48..3cbe74a1aa208cdf8f0c661a3467d91698537576 100644
--- a/telemetry/telemetry/testing/fakes/__init__.py
+++ b/telemetry/telemetry/testing/fakes/__init__.py
@@ -25,6 +25,7 @@ from telemetry.testing.internal import fake_gpu_info
 class FakePlatform(object):
   def __init__(self):
     self._network_controller = None
+    self._tracing_controller = None
 
   @property
   def is_host_platform(self):
@@ -38,7 +39,9 @@ class FakePlatform(object):
 
   @property
   def tracing_controller(self):
-    return None
+    if self._tracing_controller is None:
+      self._tracing_controller = _FakeTracingController()
+    return  self._tracing_controller
 
   def CanMonitorThermalThrottling(self):
     return False
@@ -254,6 +257,23 @@ class _FakeCredentials(object):
     pass
 
 
+class _FakeTracingController(object):
+  def __init__(self):
+    self._is_tracing = False
+
+  def StartTracing(self, tracing_config, timeout=10):
+    self._is_tracing = True
+    del tracing_config
+    del timeout
+
+  def StopTracing(self):
+    self._is_tracing = False
+
+  @property
+  def is_tracing_running(self):
+    return self._is_tracing
+
+
 class _FakeNetworkController(object):
   def __init__(self):
     self.wpr_mode = None