Add metrics for quantity and type of Favicon candidates

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 27aaf129f53b673c49140f4ff665cf9ed7b8bd98..ff27fcdc9841ef6b9ad516f456da258b9a19ff8a 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -19538,6 +19538,30 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Favicons.CandidatesCount">
+  <owner>fhorschig@chromium.org</owner>
+  <summary>
+    Records the number of favicon link tags on a page once the page has finished
+    loading. The count includes the automatically added favicon.ico entry.
+  </summary>
+</histogram>
+
+<histogram name="Favicons.CandidatesWithDefinedSizesCount">
+  <owner>fhorschig@chromium.org</owner>
+  <summary>
+    Records the number of favicon link tags with a non empty sizes attribute
+    once the page has finished loading.
+  </summary>
+</histogram>
+
+<histogram name="Favicons.CandidatesWithTouchIconsCount">
+  <owner>fhorschig@chromium.org</owner>
+  <summary>
+    Records the number of apple-touch-icon and apple-touch-icon-precomposed link
+    tags once the page has finished loading.
+  </summary>
+</histogram>
+
 <histogram name="FileBrowser.CloudImport.UserAction"
     enum="CloudImportUserAction">
   <owner>smckay@google.com</owner>