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..eeb1982c42258754f59c023bf2887bd8f77cf993 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -20427,6 +20427,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Favicons.DownloadAttempts">

[Ilya Sherman, 2017/04/12 20:43:03]

nit: Please add units="attempts"

[Ilya Sherman, 2017/04/12 20:43:03]

nit: Please add base="true", as you never record to this histogram directly;
only through suffixes.

[fhorschig, 2017/04/13 14:49:35]

Done.

[fhorschig, 2017/04/13 14:49:35]

Done.

+  <owner>fhorschig@chromium.org</owner>
+  <summary>
+    Records the number of icon requested until the best-fitting candidate was

[Ilya Sherman, 2017/04/12 20:43:03]

nit: s/icon/icons (or s/requested/requests)

[fhorschig, 2017/04/13 14:49:35]

Done.

+    found or there were no candidates left to check.
+  </summary>
+</histogram>
+
 <histogram name="FileBrowser.CloudImport.UserAction"
     enum="CloudImportUserAction">
   <owner>smckay@google.com</owner>
@@ -118846,6 +118854,13 @@ 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"