Add comment about log messages checked in autoupdate_CatchBadSignatures.

This is helpful when refactoring to avoid the newly added
autoupdate_CatchBadSignatures test failing.

BUG=chromium:264352
TEST=None (no code change.)

Change-Id: I9da0060ef99d85eaf6454c594decc0db2f6bcafd
Reviewed-on: https://chromium-review.googlesource.com/178103
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Queue: David Zeuthen <zeuthen@chromium.org>
Tested-by: David Zeuthen <zeuthen@chromium.org>
diff --git a/omaha_response_handler_action.cc b/omaha_response_handler_action.cc
index c145ae6..e54fc83 100644
--- a/omaha_response_handler_action.cc
+++ b/omaha_response_handler_action.cc
@@ -153,6 +153,8 @@
   // using an official build, so that they are protected more.
   if (!system_state_->hardware()->IsOfficialBuild()) {
     if (!response.public_key_rsa.empty()) {
+      // The autoupdate_CatchBadSignatures test checks for this string
+      // in log-files. Keep in sync.
       LOG(INFO) << "Mandating payload hash checks since Omaha Response "
                 << "for unofficial build includes public RSA key.";
       return true;