[android] Use contextlib_ext.Optional for conditional context managers.

build/android/pylib/__init__.py

Index: build/android/pylib/__init__.py
diff --git a/build/android/pylib/__init__.py b/build/android/pylib/__init__.py
index 5dc2d761da51bbd0959d8aa8d26775b0907dbb09..997a6f43145d215cc0b3020198335b55b47d9bb5 100644
--- a/build/android/pylib/__init__.py
+++ b/build/android/pylib/__init__.py
@@ -5,16 +5,17 @@
 import os
 import sys
 
-_DEVIL_PATH = os.path.abspath(os.path.join(
-    os.path.dirname(__file__), '..', '..', '..', 'third_party', 'catapult',
-    'devil'))
+_CATAPULT_PATH = os.path.abspath(os.path.join(

[rnephew (Reviews Here), 2016/12/21 16:00:56]

I'm guessing this will hit some merge conflicts with my CL that just landed, so
you'll need to rebase.

+    os.path.dirname(__file__), '..', '..', '..', 'third_party', 'catapult'))
+_DEVIL_PATH = os.path.join(_CATAPULT_PATH, 'devil')
+_PY_TRACE_EVENT_PATH = os.path.join(_CATAPULT_PATH, 'common', 'py_trace_event')
+_PY_UTILS_PATH = os.path.join(_CATAPULT_PATH, 'common', 'py_utils')
 
-_PYTRACE_PATH = os.path.abspath(os.path.join(
-    os.path.dirname(__file__), '..', '..', '..', 'third_party', 'catapult',
-    'common', 'py_trace_event'))
+if _PY_UTILS_PATH not in sys.path:
+  sys.path.append(_PY_UTILS_PATH)
 
 if _DEVIL_PATH not in sys.path:
   sys.path.append(_DEVIL_PATH)
 
-if _PYTRACE_PATH not in sys.path:
-  sys.path.append(_PYTRACE_PATH)
+if _PY_TRACE_EVENT_PATH not in sys.path:
+  sys.path.append(_PY_TRACE_EVENT_PATH)