Add UMA metrics for root scroller intervention to track forcing passive breakage.

third_party/WebKit/Source/platform/Histogram.cpp

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "platform/Histogram.h"
 
 #include "base/metrics/histogram.h"
 #include "base/metrics/sparse_histogram.h"
+#include "base/metrics/statistics_recorder.h"
 
 namespace blink {
 
 CustomCountHistogram::CustomCountHistogram(const char* name, base::HistogramBase::Sample min, base::HistogramBase::Sample max, int32_t bucketCount)
 {
     m_histogram = base::Histogram::FactoryGet(name, min, max, bucketCount, base::HistogramBase::kUmaTargetedHistogramFlag);
 }
 
 CustomCountHistogram::CustomCountHistogram(base::HistogramBase* histogram)
     : m_histogram(histogram)
 {
 }
 
 void CustomCountHistogram::count(base::HistogramBase::Sample sample)
 {
     m_histogram->Add(sample);
 }
 
 BooleanHistogram::BooleanHistogram(const char* name)
     : CustomCountHistogram(base::BooleanHistogram::FactoryGet(name, base::HistogramBase::kUmaTargetedHistogramFlag))
 {
 }
 
 EnumerationHistogram::EnumerationHistogram(const char* name, base::HistogramBase::Sample boundaryValue)
     : CustomCountHistogram(base::LinearHistogram::FactoryGet(name, 1, boundaryValue, boundaryValue + 1, base::HistogramBase::kUmaTargetedHistogramFlag))
 {
 }
 
+bool EnumerationHistogram::GetHistogramCount(const char* name, base::HistogramBase::Sample bucket, int32_t* count)
+{
+    base::HistogramBase* histogram = base::StatisticsRecorder::FindHistogram(name);
+    if (!histogram)
+        return false;
+
+    std::unique_ptr<base::HistogramSamples> samples(
+        histogram->SnapshotSamples());

[Ilya Sherman, 2016/07/11 18:52:31]

How do you guarantee that this call only includes samples from the current test,
i.e. that there's no interaction among tests?

+
+    *count = samples->GetCount(bucket);
+    return true;
+}
+
 SparseHistogram::SparseHistogram(const char* name)
 {
     m_histogram = base::SparseHistogram::FactoryGet(name, base::HistogramBase::kUmaTargetedHistogramFlag);
 }
 
 void SparseHistogram::sample(base::HistogramBase::Sample sample)
 {
     m_histogram->Add(sample);
 }
 
 } // namespace blink