update_engine: Include quick_fix_build_token in updatecheck request body

Get the value of the new device policy which is included in
AutoUpdateSettings as quick_fix_build_token, and include it
in the update request body if value is set.

BUG=chromium:932465
TEST=./build_packages --board=amd64-generic && \
     cros_run_unit_tests --board=amd64-generic --packages update_engine
Cq-Depend: chromium:1571634

Change-Id: Iaca35a08d973616a058864a11896ef9305d00174
Reviewed-on: https://chromium-review.googlesource.com/1581519
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Askar Aitzhan <askaraitzhan@google.com>
Reviewed-by: Nicolas Norvez <norvez@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
diff --git a/update_attempter.cc b/update_attempter.cc
index 44eea77..4bbf5a1 100644
--- a/update_attempter.cc
+++ b/update_attempter.cc
@@ -427,6 +427,14 @@
   omaha_request_params_->set_dlc_module_ids(dlc_module_ids_);
   omaha_request_params_->set_is_install(is_install_);
 
+  // Set Quick Fix Build token if policy is set.
+  string token;
+  if (system_state_ && system_state_->device_policy()) {
+    if (!system_state_->device_policy()->GetDeviceQuickFixBuildToken(&token))
+      token.clear();
+  }
+  omaha_request_params_->set_autoupdate_token(token);
+
   LOG(INFO) << "target_version_prefix = "
             << omaha_request_params_->target_version_prefix()
             << ", rollback_allowed = "