Add some metrics for printing with extension

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 4e8128da5b10f95847e2fc6409757a637b13f19b..a642a958c589266ceca900ec71036f58996daa3b 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -28321,6 +28321,22 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="PrintPreview.PageCount.PrintWithExtension">
+  <owner>vitalybuka@chromium.org</owner>
+  <summary>
+    The final page count (after page selection) of documents printed to an
+    extension printer (using printerProvider API).
+  </summary>
+</histogram>
+
+<histogram name="PrintPreview.PageCount.PrintWithPrivet">
+  <owner>vitalybuka@chromium.org</owner>
+  <summary>
+    The final page count (after page selection) of documents printed to a privet
+    printer.
+  </summary>
+</histogram>
+
 <histogram name="PrintPreview.PageCount.SystemDialog">
   <owner>vitalybuka@chromium.org</owner>
   <summary>
@@ -55721,6 +55737,7 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="7" label="INITIATOR_TAB_CLOSED"/>
   <int value="8" label="PRINT_WITH_CLOUD_PRINT"/>
   <int value="9" label="PRINT_WITH_PRIVET"/>
+  <int value="10" label="PRINT_WITH_EXTENSION"/>
 </enum>
 
 <enum name="PrintSettings" type="int">