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/delta_performer.cc b/delta_performer.cc
index 15f9002..eaa65d3 100644
--- a/delta_performer.cc
+++ b/delta_performer.cc
@@ -359,6 +359,8 @@
   *error = ValidateMetadataSignature(&payload[0], *metadata_size);
   if (*error != kErrorCodeSuccess) {
     if (install_plan_->hash_checks_mandatory) {
+      // The autoupdate_CatchBadSignatures test checks for this string
+      // in log-files. Keep in sync.
       LOG(ERROR) << "Mandatory metadata signature validation failed";
       return kMetadataParseError;
     }
@@ -882,6 +884,8 @@
     return kErrorCodeDownloadMetadataSignatureMismatch;
   }
 
+  // The autoupdate_CatchBadSignatures test checks for this string in
+  // log-files. Keep in sync.
   LOG(INFO) << "Metadata hash signature matches value in Omaha response.";
   return kErrorCodeSuccess;
 }
@@ -1036,6 +1040,8 @@
   TEST_AND_RETURN_VAL(kErrorCodeDownloadPayloadPubKeyVerificationError,
                       !hash_data.empty());
   if (hash_data != signed_hash_data) {
+    // The autoupdate_CatchBadSignatures test checks for this string
+    // in log-files. Keep in sync.
     LOG(ERROR) << "Public key verification failed, thus update failed. "
         "Attached Signature:";
     utils::HexDumpVector(signed_hash_data);