Prevent dummy histograms from appearing in chrome://histograms

This change removes dummy histograms in chrome://histograms

Bug: 1085912
Change-Id: I4fda6a684a20ce2effd601e78a7d601cdd29f4ac
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2214041Reviewed-by: dpapad <dpapad@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Commit-Queue: Jun Kokatsu <Jun.Kokatsu@microsoft.com>
Auto-Submit: Jun Kokatsu <Jun.Kokatsu@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#773983}

base/metrics/dummy_histogram.cc

@@ -101,10 +101,7 @@ std::unique_ptr<HistogramSamples> DummyHistogram::SnapshotFinalDelta() const {
 }
 
 base::DictionaryValue DummyHistogram::ToGraphDict() const {
-  base::DictionaryValue dict;
-  dict.SetString("header", "dummy");
-  dict.SetString("body", "dummy");
-  return dict;
+  return base::DictionaryValue();
 }
 
 }  // namespace base

base/metrics/histogram_base.h

@@ -236,7 +236,8 @@ class BASE_EXPORT HistogramBase {
   // The following method provides graphical histogram displays.
   virtual void WriteAscii(std::string* output) const = 0;
 
-  // Returns histogram data as a Dict with the following format:
+  // Returns histograms data as a Dict (or an empty dict if not available),
+  // with the following format:
   // {"header": "Name of the histogram with samples, mean, and/or flags",
   // "body": "ASCII histogram representation"}
   virtual base::DictionaryValue ToGraphDict() const = 0;

chrome/test/data/webui/histograms/histograms_internals_ui_browsertest.js

@@ -33,7 +33,7 @@ HistogramsInternalsUIBrowserTest.prototype = {
 
 TEST_F('HistogramsInternalsUIBrowserTest', 'RefreshHistograms', function() {
   test('check refresh button replaces existing histograms', function() {
-    cr.sendWithPromise('requestHistograms', '')
+    return cr.sendWithPromise('requestHistograms', '')
         .then(addHistograms)
         .finally(() => {
           const histogramHeader = 'Histogram: HTMLOut recorded 5 samples';
@@ -44,5 +44,19 @@ TEST_F('HistogramsInternalsUIBrowserTest', 'RefreshHistograms', function() {
         });
   });
 
+  mocha.run();
+});
+
+TEST_F('HistogramsInternalsUIBrowserTest', 'NoDummyHistograms', function() {
+  test('check no dummy histogram is present', function() {
+    return cr.sendWithPromise('requestHistograms', '')
+        .then(addHistograms)
+        .finally(() => {
+          document.querySelectorAll('h4').forEach(header => {
+            assertNotEquals(header.textContent, '');
+          });
+        });
+  });
+
   mocha.run();
 });
\ No newline at end of file

content/browser/histograms_internals_ui.cc

@@ -76,7 +76,8 @@ void HistogramsMessageHandler::HandleRequestHistograms(
        base::StatisticsRecorder::Sort(base::StatisticsRecorder::WithName(
            base::StatisticsRecorder::GetHistograms(), query))) {
     base::DictionaryValue histogram_dict = histogram->ToGraphDict();
-    histograms_list.Append(std::move(histogram_dict));
+    if (!histogram_dict.empty())
+      histograms_list.Append(std::move(histogram_dict));
   }
 
   ResolveJavascriptCallback(base::Value(callback_id),