Add trace events for some of telemetry internal functions

telemetry/telemetry/internal/backends/app_backend.py

Index: telemetry/telemetry/internal/backends/app_backend.py
diff --git a/telemetry/telemetry/internal/backends/app_backend.py b/telemetry/telemetry/internal/backends/app_backend.py
index c6c9bb62fae7be9540ac107d7cfdc0ea8689031b..0f33570461dd778aeca78ef553bf37e4db37c88a 100644
--- a/telemetry/telemetry/internal/backends/app_backend.py
+++ b/telemetry/telemetry/internal/backends/app_backend.py
@@ -2,8 +2,13 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+from py_trace_event import trace_event
+
 
 class AppBackend(object):
+
+  __metaclass__ = trace_event.TracedMetaClass
+
   def __init__(self, app_type, platform_backend):
     super(AppBackend, self).__init__()
     self._app = None