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

third_party/WebKit/Source/platform/Histogram.cpp

Index: third_party/WebKit/Source/platform/Histogram.cpp
diff --git a/third_party/WebKit/Source/platform/Histogram.cpp b/third_party/WebKit/Source/platform/Histogram.cpp
index cdda2dca45740c1d8e3b94f111baa2a32ed9f269..549d53beaceb61b8b16fe1c6c26c8d791988f448 100644
--- a/third_party/WebKit/Source/platform/Histogram.cpp
+++ b/third_party/WebKit/Source/platform/Histogram.cpp
@@ -6,6 +6,7 @@
 
 #include "base/metrics/histogram.h"
 #include "base/metrics/sparse_histogram.h"
+#include "base/metrics/statistics_recorder.h"
 
 namespace blink {
 
@@ -34,6 +35,19 @@ EnumerationHistogram::EnumerationHistogram(const char* name, base::HistogramBase
 {
 }
 
+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);