Add histogram for "scan credit card" usage.

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 8d39c89b1f8722c3dd3ef8742d15088a7e1ba482..9f394b93fd988a886d6943d39c98595d9d86bef4 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -1914,6 +1914,12 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <summary>TBD.</summary>
 </histogram>
 
+<histogram name="Autofill.ScanCreditCardPrompt"
+    enum="AutofillScanCreditCardPrompt">
+  <owner>estade@chromium.org</owner>
+  <summary>Usage of the &quot;Scan card&quot; control item.</summary>
+</histogram>
+
 <histogram name="Autofill.ServerExperimentId" enum="AutofillExperimentId">
   <obsolete>
     Deprecated as of 6/2011, replaced by Autofill.ServerExperimentId.Query.
@@ -41810,6 +41816,12 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="5" label="Response improves local (empty)"/>
 </enum>
 
+<enum name="AutofillScanCreditCardPrompt" type="int">
+  <int value="0" label="Scan card shown"/>
+  <int value="1" label="Scan card selected"/>
+  <int value="2" label="Some other item selected"/>
+</enum>
+
 <enum name="AutofillTypeQuality" type="int">
   <int value="0" label="Unknown"/>
   <int value="1" label="Match"/>