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/evaluation_context.cc b/update_manager/evaluation_context.cc
index 4fc9a16..a24bf23 100644
--- a/update_manager/evaluation_context.cc
+++ b/update_manager/evaluation_context.cc
@@ -20,8 +20,10 @@
 
 namespace chromeos_update_manager {
 
-EvaluationContext::EvaluationContext(ClockInterface* clock)
+EvaluationContext::EvaluationContext(ClockInterface* clock,
+                                     TimeDelta evaluation_timeout)
     : clock_(clock),
+      evaluation_timeout_(evaluation_timeout),
       weak_ptr_factory_(this) {
   ResetEvaluation();
 }