PolicyManager: New EvaluationContext class.

The EvaluationContext class handles the life of a policy request
evaluation caching all the results and tracking the variables used
by a the policy implementation.

This patch adds the first part of the EvaluationContex class with
its public interface and minimal support.

BUG=chromium:338590
TEST=Unit test added and passing.

Change-Id: I70e04e7e10ea30ddfb887b494b2b40557565b2da
Reviewed-on: https://chromium-review.googlesource.com/185106
Reviewed-by: Alex Deymo <deymo@chromium.org>
Commit-Queue: Alex Deymo <deymo@chromium.org>
Tested-by: Alex Deymo <deymo@chromium.org>
diff --git a/policy_manager/evaluation_context.cc b/policy_manager/evaluation_context.cc
new file mode 100644
index 0000000..062ed26
--- /dev/null
+++ b/policy_manager/evaluation_context.cc
@@ -0,0 +1,17 @@
+// Copyright (c) 2014 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "update_engine/policy_manager/evaluation_context.h"
+
+using base::TimeDelta;
+
+namespace chromeos_policy_manager {
+
+TimeDelta EvaluationContext::RemainingTime() const {
+  // TODO(deymo): Return a timeout based on the elapsed time on the current
+  // policy request evaluation.
+  return TimeDelta::FromSeconds(1.);
+}
+
+}  // namespace chromeos_policy_manager