update_engine: Don't require reboot after install.

We don't require a reboot after installing a DLC. Instead just set
Update Engine's status to idle.

Resubmitting now that crbug.com/905704 is fixed.

BUG=chromium:907205,chromium:907632
TEST=Attempt a DLC install, UE no longer prompts for a reboot.

(cherry picked from commit d772aaebdbd0c53d3e46e21df5783d437809108a)

Change-Id: I061ee8d6268a922ae21f310211acea5b645a3ebb
Reviewed-on: https://chromium-review.googlesource.com/1362572
Commit-Ready: Colin Howes <chowes@google.com>
Tested-by: Colin Howes <chowes@google.com>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
diff --git a/update_attempter_unittest.cc b/update_attempter_unittest.cc
index f2905bc..3209f15 100644
--- a/update_attempter_unittest.cc
+++ b/update_attempter_unittest.cc
@@ -1216,6 +1216,17 @@
   EXPECT_EQ("", attempter_.forced_omaha_url());
 }
 
+TEST_F(UpdateAttempterTest, InstallSetsStatusIdle) {
+  attempter_.CheckForInstall({}, "http://foo.bar");
+  attempter_.status_ = UpdateStatus::DOWNLOADING;
+  EXPECT_TRUE(attempter_.is_install_);
+  attempter_.ProcessingDone(nullptr, ErrorCode::kSuccess);
+  UpdateEngineStatus status;
+  attempter_.GetStatus(&status);
+  // Should set status to idle after an install operation.
+  EXPECT_EQ(UpdateStatus::IDLE, status.status);
+}
+
 TEST_F(UpdateAttempterTest, RollbackAfterInstall) {
   attempter_.is_install_ = true;
   attempter_.Rollback(false);