Add attempt count metric to FaviconHandler

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 1383139888c2b53bb63b7437a3000aa1e4c782a3..88c19cdeb9d845ad94a8a2fdd280aedb79360a24 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -20427,6 +20427,33 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Favicons.FaviconDownloadAttempts">
+  <owner>fhorschig@chromium.org</owner>
+  <summary>
+    Records the number of normal favicons requested until the best-fitting
+    candidate was found or there were no candidates left to check. The sum of
+    all Favicons.*DownloadAttempts captures all download attempts.
+  </summary>
+</histogram>
+
+<histogram name="Favicons.LargeIconDownloadAttempts">
+  <owner>fhorschig@chromium.org</owner>
+  <summary>
+    Records the number of icons requested until the largest, non-touch candidate
+    was found or there were no candidates left to check. The sum of all
+    Favicons.*DownloadAttempts captures all download attempts.
+  </summary>
+</histogram>
+
+<histogram name="Favicons.TouchIconDownloadAttempts">
+  <owner>fhorschig@chromium.org</owner>
+  <summary>
+    Records the number of icons requested until the largest, touch candidate was
+    found or there were no candidates left to check. The sum of all
+    Favicons.*DownloadAttempts captures all download attempts.
+  </summary>
+</histogram>
+
 <histogram name="FileBrowser.CloudImport.UserAction"
     enum="CloudImportUserAction">
   <owner>smckay@google.com</owner>