update_engine: Share payloads for a maximum of five days only.

This helps limit exposure of what version the device may or may not be
running.

BUG=chromium:424823
TEST=New unit test + unit tests pass.

Change-Id: I9db6f8d560e359c2b8a65d1381dc44320ed4b3a1
Reviewed-on: https://chromium-review.googlesource.com/227592
Reviewed-by: Gilad Arnold <garnold@chromium.org>
Tested-by: David Zeuthen <zeuthen@chromium.org>
Commit-Queue: David Zeuthen <zeuthen@chromium.org>
diff --git a/download_action_unittest.cc b/download_action_unittest.cc
index f241a32..78e3f5c 100644
--- a/download_action_unittest.cc
+++ b/download_action_unittest.cc
@@ -470,7 +470,9 @@
 
     // Setup p2p.
     FakeP2PManagerConfiguration *test_conf = new FakeP2PManagerConfiguration();
-    p2p_manager_.reset(P2PManager::Construct(test_conf, nullptr, "cros_au", 3));
+    p2p_manager_.reset(P2PManager::Construct(
+        test_conf, nullptr, nullptr, "cros_au", 3,
+        base::TimeDelta::FromDays(5)));
     fake_system_state_.set_p2p_manager(p2p_manager_.get());
   }