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 c867b90c99b1397d92be28ec3d1e64489fa3d7b9..8e9ef7c9d9d64e89b955a8b7caef32cce1fe46d1 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -20477,6 +20477,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram base="true" name="Favicons.DownloadAttempts" units="attempts">
+  <owner>fhorschig@chromium.org</owner>
+  <summary>
+    Records the number of icons requested until the best-fitting candidate was
+    found or there were no candidates left to check. More than 15 attempts are
+    unlikely and will be stored in overflow bucket 16. Less than 1 attempt means
+    an error happened; these cases are in bucket 0.
+  </summary>
+</histogram>
+
 <histogram name="Favicons.LargeIconService.DownloadedSize" units="pixels">
   <owner>jkrcal@chromium.org</owner>
   <summary>
@@ -119051,6 +119061,13 @@ from previous Chrome versions.
   <affected-histogram name="Extensions.ExternalExtensionEvent"/>
 </histogram_suffixes>
 
+<histogram_suffixes name="FaviconIconType" separator=".">
+  <suffix name="Favicons" label="Metrics for regular favicons."/>
+  <suffix name="LargeIcons" label="Metrics for large non-touch icons."/>
+  <suffix name="TouchIcons" label="Metrics for large touch icons."/>
+  <affected-histogram name="Favicons.DownloadAttempts"/>
+</histogram_suffixes>
+
 <histogram_suffixes name="FieldPredictionSubmissionEvents" separator=".">
   <suffix name="NoSubmission" label="No observed submission."/>
   <suffix name="BasedOnAutocomplete"