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 2594ab1e291b8407e67f72300b03cf6b45865397..78d53ab3081398848555babb0b220f4294fee739 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -20261,6 +20261,24 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Favicons.DownloadAttempts">
+  <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. See also:
+    Favicons.LargeIconDownloadAttempts for large icons.
+  </summary>
+</histogram>
+
+<histogram name="Favicons.LargeIconDownloadAttempts">
+  <owner>fhorschig@chromium.org</owner>
+  <summary>
+    Records the number of icons requested until the largest candidate was found
+    or there were no candidates left to check. See also:
+    Favicons.DownloadAttempts for all icons.
+  </summary>
+</histogram>
+
 <histogram name="FileBrowser.CloudImport.UserAction"
     enum="CloudImportUserAction">
   <owner>smckay@google.com</owner>