Implement safebrowsing download feedback service, enabled for dev & canary only.

chrome/browser/safe_browsing/two_phase_uploader.cc

Index: chrome/browser/safe_browsing/two_phase_uploader.cc
diff --git a/chrome/browser/safe_browsing/two_phase_uploader.cc b/chrome/browser/safe_browsing/two_phase_uploader.cc
index c5558d17f06d525527f86ddffb0a178c89c1481c..6fb3dc40679d1043a147b8dd4eb01df7dce9b9e8 100644
--- a/chrome/browser/safe_browsing/two_phase_uploader.cc
+++ b/chrome/browser/safe_browsing/two_phase_uploader.cc
@@ -153,7 +153,7 @@ void TwoPhaseUploaderImpl::OnURLFetchUploadProgress(
   DCHECK(CalledOnValidThread());
   DVLOG(3) << __FUNCTION__ << " " << source->GetURL().spec()
            << " " << current << "/" << total;
-  if (state_ == UPLOAD_FILE)
+  if (state_ == UPLOAD_FILE && !progress_callback_.is_null())
     progress_callback_.Run(current, total);
 }