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 31774c7ed82606dfcfe74fdb4a4a19feb94b0f78..61c60d068abf4ac8c98b4275a267a07455dacc16 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -20320,6 +20320,33 @@ 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 candidate for apple
+    touch icons 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>