Add histogram for "scan credit card" usage.

components/autofill/core/browser/autofill_external_delegate.h

Index: components/autofill/core/browser/autofill_external_delegate.h
diff --git a/components/autofill/core/browser/autofill_external_delegate.h b/components/autofill/core/browser/autofill_external_delegate.h
index ed745e0a78b2a31877e383f2c87e400ccbe7c484..f90daf6bd7b2a8f3e08886fe9bdd0260e1b7efb6 100644
--- a/components/autofill/core/browser/autofill_external_delegate.h
+++ b/components/autofill/core/browser/autofill_external_delegate.h
@@ -153,14 +153,17 @@ class AutofillExternalDelegate : public AutofillPopupDelegate {
   // currently editing?  Used to keep track of state for metrics logging.
   bool has_shown_popup_for_current_edit_;
 
-  // The current data list values.
-  std::vector<base::string16> data_list_values_;
-  std::vector<base::string16> data_list_labels_;
+  // FIXME

[Justin Donnelly, 2015/11/16 20:23:28]

Just noticed this. I assume you meant to add a comment here?

[Evan Stade, 2015/11/16 20:43:53]

oops. Yes, that was the intent.

+  bool should_show_scan_credit_card_;
 
   // Whether the access Address Book prompt has ever been shown for the current
   // |query_form_|. This variable is only used on OSX.
   bool has_shown_address_book_prompt;
 
+  // The current data list values.
+  std::vector<base::string16> data_list_values_;
+  std::vector<base::string16> data_list_labels_;
+
   base::WeakPtrFactory<AutofillExternalDelegate> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(AutofillExternalDelegate);