UM: Make the evaluation timeout configurable.

This allows the client to construct the UpdateManager with a custom
evaluation timeout for sync policy requests, which is in turn being
passed to each EvaluationContext instance used for sync policy
evaluation.

BUG=chromium:363790
TEST=Unit tests.

Change-Id: I5a6ec02a3ca2a2c611276eacbcda6aac8304e929
Reviewed-on: https://chromium-review.googlesource.com/204687
Reviewed-by: Gilad Arnold <garnold@chromium.org>
Commit-Queue: Gilad Arnold <garnold@chromium.org>
Tested-by: Gilad Arnold <garnold@chromium.org>
diff --git a/update_manager/chromeos_policy_unittest.cc b/update_manager/chromeos_policy_unittest.cc
index 140b6ba..6c6eeff 100644
--- a/update_manager/chromeos_policy_unittest.cc
+++ b/update_manager/chromeos_policy_unittest.cc
@@ -30,7 +30,7 @@
  protected:
   virtual void SetUp() {
     SetUpDefaultClock();
-    eval_ctx_ = new EvaluationContext(&fake_clock_);
+    eval_ctx_ = new EvaluationContext(&fake_clock_, TimeDelta::FromSeconds(5));
     SetUpDefaultState();
     SetUpDefaultDevicePolicy();
   }