[translate] Declare additional timers in histograms.xml.

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 3862a2a74878c1b5548e0c7d4fd1ea39742e0ae0..e6e560124042ac599d612739a0889de5336fcc3e 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -76088,14 +76088,23 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 <histogram name="Translate.Ranker.Timer.DownloadModel" units="ms">
   <owner>rogerm@google.com</owner>
   <summary>
-    Time taken for the TranslateRanker to download its model, in ms.
+    Time taken for the Translate Ranker Model Loader to download its model from
+    the configured URL, in ms.
   </summary>
 </histogram>
 
 <histogram name="Translate.Ranker.Timer.ParseModel" units="ms">
   <owner>rogerm@google.com</owner>
   <summary>
-    Time taken for the TranslateRanker to parse its model, in ms.
+    Time taken for the Translate Ranker Model Loader to parse its model, in ms.
+  </summary>
+</histogram>
+
+<histogram name="Translate.Ranker.Timer.ReadModel" units="ms">
+  <owner>rogerm@google.com</owner>
+  <summary>
+    Time taken for the Translate Ranker Model Loader to read its model from
+    local storage (cache), in ms.
   </summary>
 </histogram>
 
@@ -76109,6 +76118,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Translate.Ranker.Timer.WriteModel" units="ms">
+  <owner>rogerm@google.com</owner>
+  <summary>
+    Time taken for the Translate Ranker Model Loader to write its model to local
+    storage, in ms.
+  </summary>
+</histogram>
+
 <histogram name="Translate.ReportLanguageDetectionError">
   <owner>kenjibaheux@google.com</owner>
   <summary>