update_attempter: Set is_install_ to false when doing a rollback.

We weren't setting is_install_ when performing a rollback, meaning it
was potentially left uninitialized or had a stale value from a previous
install/update attempt. Explicitly set is_install_ in Rollback() and in
the UpdateAttempter constructor.

BUG=chromium:905704
TEST=Add a unittest.

Change-Id: I19b646d689cab869a2aca0cd82def252c370184b
Reviewed-on: https://chromium-review.googlesource.com/1359109
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 a395e1b..f2905bc 100644
--- a/update_attempter_unittest.cc
+++ b/update_attempter_unittest.cc
@@ -1216,6 +1216,18 @@
   EXPECT_EQ("", attempter_.forced_omaha_url());
 }
 
+TEST_F(UpdateAttempterTest, RollbackAfterInstall) {
+  attempter_.is_install_ = true;
+  attempter_.Rollback(false);
+  EXPECT_FALSE(attempter_.is_install_);
+}
+
+TEST_F(UpdateAttempterTest, UpdateAfterInstall) {
+  attempter_.is_install_ = true;
+  attempter_.CheckForUpdate("", "", UpdateAttemptFlags::kNone);
+  EXPECT_FALSE(attempter_.is_install_);
+}
+
 TEST_F(UpdateAttempterTest, TargetVersionPrefixSetAndReset) {
   attempter_.CalculateUpdateParams("", "", "", "1234", false, false, false);
   EXPECT_EQ("1234",