Measure whether muted videos that started playing with play() become visible at some point

third_party/WebKit/Source/core/html/AutoplayUmaHelper.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 "core/html/AutoplayUmaHelper.h"
+
+#include "core/html/HTMLMediaElement.h"
+#include "platform/Histogram.h"
+
+namespace blink {
+
+namespace {
+
+    void recordMutedVideoOfSourceMethodFinallyVisibleUma(bool visible)
+    {
+        DEFINE_STATIC_LOCAL(BooleanHistogram, histogram, ("Media.Video.Autoplay.Muted.SourceMethod.FinallyVisible"));
+        histogram.count(visible);
+    }

[mlamouri (slow - plz ping), 2016/07/01 11:00:07]

style: no indentation

[Zhiqiang Zhang (Slow), 2016/07/04 14:34:38]

Done.

+
+} // namespace
+
+AutoplayUmaHelper::AutoplayUmaHelper(HTMLMediaElement* element)
+    : m_source(AutoplaySource::NumberOfSources)
+    , m_element(element)
+{
+}
+
+AutoplayUmaHelper::~AutoplayUmaHelper() = default;
+
+void AutoplayUmaHelper::onAutoplayInitiated(AutoplaySource source)
+{
+    m_source = source;
+}
+
+void AutoplayUmaHelper::onAutoplayStarted()
+{
+    if (m_source == AutoplaySource::Method && m_element->isHTMLVideoElement() && m_element->muted())
+        recordMutedVideoOfSourceMethodFinallyVisibleUma(true);
+}
+
+void AutoplayUmaHelper::onElementDestroyed()

[mlamouri (slow - plz ping), 2016/07/01 11:00:07]

The issue with recording UMA in a dtor is that it might not work very well. I
would make sure the uma description say that.

[Zhiqiang Zhang (Slow), 2016/07/04 14:34:38]

Done.

+{
+    if (m_source == AutoplaySource::Method && m_element->isHTMLVideoElement() && m_element->muted())
+        recordMutedVideoOfSourceMethodFinallyVisibleUma(false);

[mlamouri (slow - plz ping), 2016/07/01 11:00:07]

Maybe you could have a `m_shouldRecordVisibilityChange` boolean to keep track of
this state?

[Zhiqiang Zhang (Slow), 2016/07/04 14:34:38]

The logic here was wrong. I'm using a ElementVisibilityObserver to keep track of
videos autoplaying muted by play() method. Doing a null check on the observer
should be enough.

+}
+
+DEFINE_TRACE(AutoplayUmaHelper)
+{
+    visitor->trace(m_element);
+}
+
+} // namespace blink