Add DownloadStatus metric to FaviconHandler

components/favicon/core/favicon_handler.cc

Index: components/favicon/core/favicon_handler.cc
diff --git a/components/favicon/core/favicon_handler.cc b/components/favicon/core/favicon_handler.cc
index 79f35f0622513060931374b18488cf052049e147..ef809b0cb6d2431959161c0593aeca7115421d47 100644
--- a/components/favicon/core/favicon_handler.cc
+++ b/components/favicon/core/favicon_handler.cc
@@ -382,12 +382,16 @@ void FaviconHandler::OnDidDownloadFavicon(
 
   if (bitmaps.empty() && http_status_code == 404) {
     DVLOG(1) << "Failed to Download Favicon:" << image_url;
+    UMA_HISTOGRAM_COUNTS_100("Favicons.DownloadOutcome",

[Ilya Sherman, 2017/04/12 23:22:13]

Could this be UMA_HISTOGRAM_SPARSE_SLOWLY or UMA_HISTOGRAM_ENUMERATION? 
UMA_HISTOGRAM_COUNTS_100 does not seem appropriate for this purpose.

[fhorschig, 2017/04/13 15:14:05]

Done.

+                             DownloadOutcome::FAILED);
     if (service_)
       service_->UnableToDownloadFavicon(image_url);
   }
 
   bool request_next_icon = true;
   if (!bitmaps.empty()) {
+    UMA_HISTOGRAM_COUNTS_100("Favicons.DownloadOutcome",
+                             DownloadOutcome::SUCCEEDED);

[Ilya Sherman, 2017/04/12 23:22:13]

Please create a small wrapper function for emitting to this histogram, so that
you do not need to repeat the macro invocation several times.  The macro expands
to a fair bit of code, so it's nice to help the compiler avoid doing that
multiple times.

[fhorschig, 2017/04/13 15:14:05]

Done, thanks for the explanation!

     float score = 0.0f;
     gfx::ImageSkia image_skia;
     if (download_largest_icon_) {
@@ -557,6 +561,8 @@ void FaviconHandler::ScheduleDownload(const GURL& image_url,
   DCHECK(download_request_.IsCancelled()) << "More than one ongoing download";
   if (service_ && service_->WasUnableToDownloadFavicon(image_url)) {
     DVLOG(1) << "Skip Failed FavIcon: " << image_url;
+    UMA_HISTOGRAM_COUNTS_100("Favicons.DownloadOutcome",
+                             DownloadOutcome::SKIPPED);
     OnDidDownloadFavicon(icon_type, 0, 0, image_url, std::vector<SkBitmap>(),
                          std::vector<gfx::Size>());
     return;