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)

[Rick Byers, 2016/07/11 14:41:52]

Probably want someone from uma-team to take a look at the testing strategy here.
 Does this mirror what's already done for histogram testing outside blink?  Eg.
I'm wondering if we should be clear that these functions are intended just for
testing.

[dtapuska, 2016/07/11 15:46:05]

isherman@ can you comment on this? (It is pretty much the same as
HistogramTester class.

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

Yeah, the HistogramTester class [1] is what's used elsewhere in Chromium for
testing histograms.  It would be best if we could reuse that implementation. 
Note that the HistogramTester class does some work to initialize the
StatisticsRecorded, and ensure that each test sees deltas that are only based on
the code under test -- it essentially works as a scoped object.  I'm a little
concerned that the approach you have currently implemented will allow
dependencies across tests to form, because the metrics system is basically a
shared global object, and I don't see any code here that compensates for that.

[1] https://cs.chromium.org/chromium/src/base/test/histogram_tester.h

+{
+    base::HistogramBase* histogram = base::StatisticsRecorder::FindHistogram(name);
+    if (!histogram)
+        return false;
+
+    std::unique_ptr<base::HistogramSamples> samples(
+        histogram->SnapshotSamples());
+
+    *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