Add a histogram to track the type of documents printed (HTML vs PDF)

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 56a2c095ca089f23d7043c79d92f9549ee76a537..4e89e17cd03bc7460b71b94ca67edf417a244331 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -50204,6 +50204,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>Print preview events.</summary>
 </histogram>
 
+<histogram name="PrintPreview.PrintDocumentType"
+    enum="PrintPreviewPrintDocumentTypeBuckets">
+  <owner>rbpotter@chromium.org</owner>
+  <summary>
+    Track type of documents printed (HTML vs PDF). Recorded immediately after a
+    user requests that a document be printed.
+  </summary>
+</histogram>
+
 <histogram name="PrintPreview.PrintSettings" enum="PrintSettings">
   <owner>vitalybuka@chromium.org</owner>
   <summary>
@@ -99956,6 +99965,11 @@ value.
   <int value="13" label="INVITATION_REJECTED"/>
 </enum>
 
+<enum name="PrintPreviewPrintDocumentTypeBuckets" type="int">
+  <int value="0" label="HTML_DOCUMENT"/>
+  <int value="1" label="PDF_DOCUMENT"/>
+</enum>
+
 <enum name="PrintPreviewPrintSettingsUiBuckets" type="int">
   <int value="0" label="ADVANCED_SETTINGS_DIALOG_SHOWN"/>
   <int value="1" label="ADVANCED_SETTINGS_DIALOG_CANCELED"/>