Count external PDF viewer usage in print preview.

chrome/browser/ui/webui/print_preview/print_preview_handler.cc

Index: chrome/browser/ui/webui/print_preview/print_preview_handler.cc
diff --git a/chrome/browser/ui/webui/print_preview/print_preview_handler.cc b/chrome/browser/ui/webui/print_preview/print_preview_handler.cc
index ffc06bd089d6371bb2aa9bbbeff82f68363a3aa5..27ab250de074ecbe1b6280cc66eac14b10c78c11 100644
--- a/chrome/browser/ui/webui/print_preview/print_preview_handler.cc
+++ b/chrome/browser/ui/webui/print_preview/print_preview_handler.cc
@@ -118,6 +118,7 @@ enum PrintSettingsBuckets {
   HEADERS_AND_FOOTERS,
   CSS_BACKGROUND,
   SELECTION_ONLY,
+  EXTERNAL_PDF_PREVIEW,
   PRINT_SETTINGS_BUCKET_BOUNDARY
 };
 
@@ -261,6 +262,12 @@ void ReportPrintSettingsStats(const base::DictionaryValue& settings) {
                           &selection_only) && selection_only) {
     ReportPrintSettingHistogram(SELECTION_ONLY);
   }
+
+  bool external_preview = false;
+  if (settings.GetBoolean(printing::kSettingOpenPDFInPreview,
+                          &external_preview) && external_preview) {
+    ReportPrintSettingHistogram(EXTERNAL_PDF_PREVIEW);
+  }
 }
 
 // Callback that stores a PDF file on disk.