update_engine: Log when EOL date is set + retrieved

autoupdate_EOL autotests seems to fail and return a default EOL date
value of -9999. This logging helps pinpoint whether prefs are the
culprit.

BUG=chromium:1090283
TEST=FEATURES=test emerge-$B update_engine update_engine-client

Change-Id: If2feb4841d2642af89dac94e699a30a7ee2fb002
Reviewed-on: https://chromium-review.googlesource.com/c/aosp/platform/system/update_engine/+/2227031
Tested-by: Jae Hoon Kim <kimjae@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
Auto-Submit: Jae Hoon Kim <kimjae@chromium.org>
Commit-Queue: Jae Hoon Kim <kimjae@chromium.org>
diff --git a/omaha_request_action.cc b/omaha_request_action.cc
index 8728f72..86d4b93 100644
--- a/omaha_request_action.cc
+++ b/omaha_request_action.cc
@@ -1366,11 +1366,13 @@
   // If EOL date attribute is not sent, don't delete the old persisted EOL
   // date information.
   auto eol_date_attr = attrs.find(kAttrEolDate);
-  if (eol_date_attr != attrs.end() &&
-      !system_state_->prefs()->SetString(kPrefsOmahaEolDate,
-                                         eol_date_attr->second)) {
-    LOG(ERROR) << "Setting EOL date failed.";
-    return false;
+  if (eol_date_attr != attrs.end()) {
+    const auto& eol_date = eol_date_attr->second;
+    if (!system_state_->prefs()->SetString(kPrefsOmahaEolDate, eol_date)) {
+      LOG(ERROR) << "Setting EOL date failed.";
+      return false;
+    }
+    LOG(INFO) << "Set EOL date to " << eol_date;
   }
   return true;
 }