add UMA to record if a page has distilled data.

BUG=418190

Review URL: https://codereview.chromium.org/607013003

Cr-Commit-Position: refs/heads/master@{#297100}

components/dom_distiller/core/viewer.cc

@@ -9,6 +9,7 @@
 
 #include "base/json/json_writer.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/metrics/histogram.h"
 #include "base/strings/string_util.h"
 #include "components/dom_distiller/core/distilled_page_prefs.h"
 #include "components/dom_distiller/core/dom_distiller_service.h"
@@ -92,6 +93,7 @@ const std::string GetFontCssClass(DistilledPagePrefs::FontFamily font_family) {
 void EnsureNonEmptyTitleAndContent(std::string* title, std::string* content) {
   if (title->empty())
     *title = l10n_util::GetStringUTF8(IDS_DOM_DISTILLER_VIEWER_NO_DATA_TITLE);
+  UMA_HISTOGRAM_BOOLEAN("DomDistiller.PageHasDistilledData", !content->empty());
   if (content->empty()) {
     *content = l10n_util::GetStringUTF8(
         IDS_DOM_DISTILLER_VIEWER_NO_DATA_CONTENT);

tools/metrics/histograms/histograms.xml

@@ -5113,6 +5113,12 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="DomDistiller.PageHasDistilledData"
+    enum="BooleanHasDistilledData">
+  <owner>kuan@chromium.org</owner>
+  <summary>Records whether a page has distilled data.</summary>
+</histogram>
+
 <histogram name="DomDistiller.Statistics.WordCount" units="words">
   <owner>nyquist@chromium.org</owner>
   <summary>
@@ -39124,6 +39130,11 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="1" label="Has CRC"/>
 </enum>
 
+<enum name="BooleanHasDistilledData" type="int">
+  <int value="0" label="No distilled data"/>
+  <int value="1" label="Has distilled data"/>
+</enum>
+
 <enum name="BooleanHit" type="int">
   <int value="0" label="Not_reached"/>
   <int value="1" label="Hit"/>