[Android] Add a configurable environment for devil/. (RELAND 2)

build/android/devil/utils/lazy/weak_constant.py

+# Copyright 2015 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 threading
+
+
+class WeakConstant(object):
+  """A thread-safe, lazily initialized object.
+
+  This does not support modification after initialization. The intended
+  constant nature of the object is not enforced, though, hence the "weak".
+  """
+
+  def __init__(self, initializer):
+    self._initialized = False
+    self._initializer = initializer
+    self._lock = threading.Lock()
+    self._val = None
+
+  def read(self):
+    """Get the object, creating it if necessary."""
+    if self._initialized:
+      return self._val
+    with self._lock:
+      if not self._initialized:
+        self._val = self._initializer()
+        self._initialized = True
+    return self._val